* [PATCH v11 1/7] cgroup: switch to unsigned long for bitmasks
2015-05-16 4:13 [PATCH v11 0/7] cgroups: add pids subsystem Aleksa Sarai
@ 2015-05-16 4:13 ` Aleksa Sarai
2015-05-16 4:13 ` [PATCH v11 2/7] cgroup: use bitmask to filter for_each_subsys Aleksa Sarai
` (5 subsequent siblings)
6 siblings, 0 replies; 11+ messages in thread
From: Aleksa Sarai @ 2015-05-16 4:13 UTC (permalink / raw)
To: tj, lizefan, mingo, peterz
Cc: richard, fweisbec, linux-kernel, cgroups, Aleksa Sarai
Switch the type of all internal cgroup masks to (unsigned long), which
is the correct type for bitmasks. This is in preparation for the
for_each_subsys_which patch.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
kernel/cgroup.c | 39 ++++++++++++++++++++-------------------
1 file changed, 20 insertions(+), 19 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 469dd54..15896ed 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -156,7 +156,7 @@ static bool cgrp_dfl_root_visible;
static bool cgroup_legacy_files_on_dfl;
/* some controllers are not supported in the default hierarchy */
-static unsigned int cgrp_dfl_root_inhibit_ss_mask;
+static unsigned long cgrp_dfl_root_inhibit_ss_mask;
/* The list of hierarchy roots */
@@ -186,7 +186,7 @@ static struct cftype cgroup_dfl_base_files[];
static struct cftype cgroup_legacy_base_files[];
static int rebind_subsystems(struct cgroup_root *dst_root,
- unsigned int ss_mask);
+ unsigned long ss_mask);
static int cgroup_destroy_locked(struct cgroup *cgrp);
static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
bool visible);
@@ -998,7 +998,7 @@ static struct cgroup *task_cgroup_from_root(struct task_struct *task,
* update of a tasks cgroup pointer by cgroup_attach_task()
*/
-static int cgroup_populate_dir(struct cgroup *cgrp, unsigned int subsys_mask);
+static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask);
static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
static const struct file_operations proc_cgroupstats_operations;
@@ -1068,11 +1068,11 @@ static void cgroup_put(struct cgroup *cgrp)
* @subtree_control is to be applied to @cgrp. The returned mask is always
* a superset of @subtree_control and follows the usual hierarchy rules.
*/
-static unsigned int cgroup_calc_child_subsys_mask(struct cgroup *cgrp,
- unsigned int subtree_control)
+static unsigned long cgroup_calc_child_subsys_mask(struct cgroup *cgrp,
+ unsigned long subtree_control)
{
struct cgroup *parent = cgroup_parent(cgrp);
- unsigned int cur_ss_mask = subtree_control;
+ unsigned long cur_ss_mask = subtree_control;
struct cgroup_subsys *ss;
int ssid;
@@ -1082,7 +1082,7 @@ static unsigned int cgroup_calc_child_subsys_mask(struct cgroup *cgrp,
return cur_ss_mask;
while (true) {
- unsigned int new_ss_mask = cur_ss_mask;
+ unsigned long new_ss_mask = cur_ss_mask;
for_each_subsys(ss, ssid)
if (cur_ss_mask & (1 << ssid))
@@ -1200,7 +1200,7 @@ static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
* @cgrp: target cgroup
* @subsys_mask: mask of the subsystem ids whose files should be removed
*/
-static void cgroup_clear_dir(struct cgroup *cgrp, unsigned int subsys_mask)
+static void cgroup_clear_dir(struct cgroup *cgrp, unsigned long subsys_mask)
{
struct cgroup_subsys *ss;
int i;
@@ -1215,10 +1215,11 @@ static void cgroup_clear_dir(struct cgroup *cgrp, unsigned int subsys_mask)
}
}
-static int rebind_subsystems(struct cgroup_root *dst_root, unsigned int ss_mask)
+static int rebind_subsystems(struct cgroup_root *dst_root,
+ unsigned long ss_mask)
{
struct cgroup_subsys *ss;
- unsigned int tmp_ss_mask;
+ unsigned long tmp_ss_mask;
int ssid, i, ret;
lockdep_assert_held(&cgroup_mutex);
@@ -1253,7 +1254,7 @@ static int rebind_subsystems(struct cgroup_root *dst_root, unsigned int ss_mask)
* Just warn about it and continue.
*/
if (cgrp_dfl_root_visible) {
- pr_warn("failed to create files (%d) while rebinding 0x%x to default root\n",
+ pr_warn("failed to create files (%d) while rebinding 0x%lx to default root\n",
ret, ss_mask);
pr_warn("you may retry by moving them to a different hierarchy and unbinding\n");
}
@@ -1338,7 +1339,7 @@ static int cgroup_show_options(struct seq_file *seq,
}
struct cgroup_sb_opts {
- unsigned int subsys_mask;
+ unsigned long subsys_mask;
unsigned int flags;
char *release_agent;
bool cpuset_clone_children;
@@ -1351,7 +1352,7 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
{
char *token, *o = data;
bool all_ss = false, one_ss = false;
- unsigned int mask = -1U;
+ unsigned long mask = -1UL;
struct cgroup_subsys *ss;
int nr_opts = 0;
int i;
@@ -1495,7 +1496,7 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
int ret = 0;
struct cgroup_root *root = cgroup_root_from_kf(kf_root);
struct cgroup_sb_opts opts;
- unsigned int added_mask, removed_mask;
+ unsigned long added_mask, removed_mask;
if (root == &cgrp_dfl_root) {
pr_err("remount is not allowed\n");
@@ -1641,7 +1642,7 @@ static void init_cgroup_root(struct cgroup_root *root,
set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
}
-static int cgroup_setup_root(struct cgroup_root *root, unsigned int ss_mask)
+static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask)
{
LIST_HEAD(tmp_links);
struct cgroup *root_cgrp = &root->cgrp;
@@ -2542,7 +2543,7 @@ static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
return 0;
}
-static void cgroup_print_ss_mask(struct seq_file *seq, unsigned int ss_mask)
+static void cgroup_print_ss_mask(struct seq_file *seq, unsigned long ss_mask)
{
struct cgroup_subsys *ss;
bool printed = false;
@@ -2689,8 +2690,8 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
char *buf, size_t nbytes,
loff_t off)
{
- unsigned int enable = 0, disable = 0;
- unsigned int css_enable, css_disable, old_sc, new_sc, old_ss, new_ss;
+ unsigned long enable = 0, disable = 0;
+ unsigned long css_enable, css_disable, old_sc, new_sc, old_ss, new_ss;
struct cgroup *cgrp, *child;
struct cgroup_subsys *ss;
char *tok;
@@ -4322,7 +4323,7 @@ static struct cftype cgroup_legacy_base_files[] = {
*
* On failure, no file is added.
*/
-static int cgroup_populate_dir(struct cgroup *cgrp, unsigned int subsys_mask)
+static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask)
{
struct cgroup_subsys *ss;
int i, ret = 0;
--
2.4.1
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v11 2/7] cgroup: use bitmask to filter for_each_subsys
2015-05-16 4:13 [PATCH v11 0/7] cgroups: add pids subsystem Aleksa Sarai
2015-05-16 4:13 ` [PATCH v11 1/7] cgroup: switch to unsigned long for bitmasks Aleksa Sarai
@ 2015-05-16 4:13 ` Aleksa Sarai
2015-05-16 4:13 ` [PATCH v11 3/7] cgroup: replace explicit ss_mask checking with for_each_subsys_which Aleksa Sarai
` (4 subsequent siblings)
6 siblings, 0 replies; 11+ messages in thread
From: Aleksa Sarai @ 2015-05-16 4:13 UTC (permalink / raw)
To: tj, lizefan, mingo, peterz
Cc: richard, fweisbec, linux-kernel, cgroups, Aleksa Sarai
Add a new macro for_each_subsys_which that allows all enabled cgroup
subsystems to be filtered by a bitmask, such that mask & (1 << ssid)
determines if the subsystem is to be processed in the loop body (where
ssid is the unique id of the subsystem).
Also replace the need_forkexit_callback with two separate bitmasks for
each callback to make (ss->{fork,exit}) checks unnecessary.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
kernel/cgroup.c | 46 +++++++++++++++++++++++++++++-----------------
1 file changed, 29 insertions(+), 17 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 15896ed..633d02a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -175,12 +175,14 @@ static DEFINE_IDR(cgroup_hierarchy_idr);
*/
static u64 css_serial_nr_next = 1;
-/* This flag indicates whether tasks in the fork and exit paths should
+/*
+ * These bitmask flags indicate whether tasks in the fork and exit paths should
* check for fork/exit handlers to call. This avoids us having to do
* extra work in the fork/exit path if none of the subsystems need to
* be called.
*/
-static int need_forkexit_callback __read_mostly;
+static unsigned long have_fork_callback __read_mostly;
+static unsigned long have_exit_callback __read_mostly;
static struct cftype cgroup_dfl_base_files[];
static struct cftype cgroup_legacy_base_files[];
@@ -409,6 +411,22 @@ static int notify_on_release(const struct cgroup *cgrp)
for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT && \
(((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
+
+/**
+ * for_each_subsys_which - filter for_each_subsys with a bitmask
+ * @ss: the iteration cursor
+ * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
+ * @ss_maskp: a pointer to the bitmask
+ *
+ * The block will only run for cases where the ssid-th bit (1 << ssid) of
+ * mask is set to 1.
+ */
+#define for_each_subsys_which(ss, ssid, ss_maskp) \
+ for_each_set_bit(ssid, ss_maskp, CGROUP_SUBSYS_COUNT) \
+ if (((ss) = cgroup_subsys[ssid]) && false) \
+ ; \
+ else
+
/* iterate across the hierarchies */
#define for_each_root(root) \
list_for_each_entry((root), &cgroup_roots, root_list)
@@ -4932,7 +4950,8 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
* init_css_set is in the subsystem's root cgroup. */
init_css_set.subsys[ss->id] = css;
- need_forkexit_callback |= ss->fork || ss->exit;
+ have_fork_callback |= (bool)ss->fork << ss->id;
+ have_exit_callback |= (bool)ss->exit << ss->id;
/* At system boot, before all subsystems have been
* registered, no tasks have been forked, so we don't
@@ -5242,11 +5261,8 @@ void cgroup_post_fork(struct task_struct *child)
* css_set; otherwise, @child might change state between ->fork()
* and addition to css_set.
*/
- if (need_forkexit_callback) {
- for_each_subsys(ss, i)
- if (ss->fork)
- ss->fork(child);
- }
+ for_each_subsys_which(ss, i, &have_fork_callback)
+ ss->fork(child);
}
/**
@@ -5290,16 +5306,12 @@ void cgroup_exit(struct task_struct *tsk)
cset = task_css_set(tsk);
RCU_INIT_POINTER(tsk->cgroups, &init_css_set);
- if (need_forkexit_callback) {
- /* see cgroup_post_fork() for details */
- for_each_subsys(ss, i) {
- if (ss->exit) {
- struct cgroup_subsys_state *old_css = cset->subsys[i];
- struct cgroup_subsys_state *css = task_css(tsk, i);
+ /* see cgroup_post_fork() for details */
+ for_each_subsys_which(ss, i, &have_exit_callback) {
+ struct cgroup_subsys_state *old_css = cset->subsys[i];
+ struct cgroup_subsys_state *css = task_css(tsk, i);
- ss->exit(css, old_css, tsk);
- }
- }
+ ss->exit(css, old_css, tsk);
}
if (put_cset)
--
2.4.1
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v11 3/7] cgroup: replace explicit ss_mask checking with for_each_subsys_which
2015-05-16 4:13 [PATCH v11 0/7] cgroups: add pids subsystem Aleksa Sarai
2015-05-16 4:13 ` [PATCH v11 1/7] cgroup: switch to unsigned long for bitmasks Aleksa Sarai
2015-05-16 4:13 ` [PATCH v11 2/7] cgroup: use bitmask to filter for_each_subsys Aleksa Sarai
@ 2015-05-16 4:13 ` Aleksa Sarai
2015-05-16 4:13 ` [PATCH v11 4/7] cgroup, block: implement task_get_css() and use it in bio_associate_current() Aleksa Sarai
` (3 subsequent siblings)
6 siblings, 0 replies; 11+ messages in thread
From: Aleksa Sarai @ 2015-05-16 4:13 UTC (permalink / raw)
To: tj, lizefan, mingo, peterz
Cc: richard, fweisbec, linux-kernel, cgroups, Aleksa Sarai
Replace the explicit checking against ss_masks inside a for_each_subsys
block with for_each_subsys_which(..., ss_mask), to take advantage of the
more readable macro.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
kernel/cgroup.c | 44 ++++++++++++++++----------------------------
1 file changed, 16 insertions(+), 28 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 633d02a..eb5e4b3 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1102,9 +1102,8 @@ static unsigned long cgroup_calc_child_subsys_mask(struct cgroup *cgrp,
while (true) {
unsigned long new_ss_mask = cur_ss_mask;
- for_each_subsys(ss, ssid)
- if (cur_ss_mask & (1 << ssid))
- new_ss_mask |= ss->depends_on;
+ for_each_subsys_which(ss, ssid, &cur_ss_mask)
+ new_ss_mask |= ss->depends_on;
/*
* Mask out subsystems which aren't available. This can
@@ -1242,10 +1241,7 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
lockdep_assert_held(&cgroup_mutex);
- for_each_subsys(ss, ssid) {
- if (!(ss_mask & (1 << ssid)))
- continue;
-
+ for_each_subsys_which(ss, ssid, &ss_mask) {
/* if @ss has non-root csses attached to it, can't move */
if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)))
return -EBUSY;
@@ -1282,18 +1278,14 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
* Nothing can fail from this point on. Remove files for the
* removed subsystems and rebind each subsystem.
*/
- for_each_subsys(ss, ssid)
- if (ss_mask & (1 << ssid))
- cgroup_clear_dir(&ss->root->cgrp, 1 << ssid);
+ for_each_subsys_which(ss, ssid, &ss_mask)
+ cgroup_clear_dir(&ss->root->cgrp, 1 << ssid);
- for_each_subsys(ss, ssid) {
+ for_each_subsys_which(ss, ssid, &ss_mask) {
struct cgroup_root *src_root;
struct cgroup_subsys_state *css;
struct css_set *cset;
- if (!(ss_mask & (1 << ssid)))
- continue;
-
src_root = ss->root;
css = cgroup_css(&src_root->cgrp, ss);
@@ -2567,13 +2559,11 @@ static void cgroup_print_ss_mask(struct seq_file *seq, unsigned long ss_mask)
bool printed = false;
int ssid;
- for_each_subsys(ss, ssid) {
- if (ss_mask & (1 << ssid)) {
- if (printed)
- seq_putc(seq, ' ');
- seq_printf(seq, "%s", ss->name);
- printed = true;
- }
+ for_each_subsys_which(ss, ssid, &ss_mask) {
+ if (printed)
+ seq_putc(seq, ' ');
+ seq_printf(seq, "%s", ss->name);
+ printed = true;
}
if (printed)
seq_putc(seq, '\n');
@@ -2721,11 +2711,12 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
*/
buf = strstrip(buf);
while ((tok = strsep(&buf, " "))) {
+ unsigned long tmp_ss_mask = ~cgrp_dfl_root_inhibit_ss_mask;
+
if (tok[0] == '\0')
continue;
- for_each_subsys(ss, ssid) {
- if (ss->disabled || strcmp(tok + 1, ss->name) ||
- ((1 << ss->id) & cgrp_dfl_root_inhibit_ss_mask))
+ for_each_subsys_which(ss, ssid, &tmp_ss_mask) {
+ if (ss->disabled || strcmp(tok + 1, ss->name))
continue;
if (*tok == '+') {
@@ -2812,10 +2803,7 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
* still around. In such cases, wait till it's gone using
* offline_waitq.
*/
- for_each_subsys(ss, ssid) {
- if (!(css_enable & (1 << ssid)))
- continue;
-
+ for_each_subsys_which(ss, ssid, &css_enable) {
cgroup_for_each_live_child(child, cgrp) {
DEFINE_WAIT(wait);
--
2.4.1
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v11 4/7] cgroup, block: implement task_get_css() and use it in bio_associate_current()
2015-05-16 4:13 [PATCH v11 0/7] cgroups: add pids subsystem Aleksa Sarai
` (2 preceding siblings ...)
2015-05-16 4:13 ` [PATCH v11 3/7] cgroup: replace explicit ss_mask checking with for_each_subsys_which Aleksa Sarai
@ 2015-05-16 4:13 ` Aleksa Sarai
2015-05-16 4:13 ` [PATCH v11 5/7] cgroup: move enum cgroup_subsys_id definition Aleksa Sarai
` (2 subsequent siblings)
6 siblings, 0 replies; 11+ messages in thread
From: Aleksa Sarai @ 2015-05-16 4:13 UTC (permalink / raw)
To: tj, lizefan, mingo, peterz
Cc: richard, fweisbec, linux-kernel, cgroups, Jens Axboe, Vivek Goyal
From: Tejun Heo <tj@kernel.org>
bio_associate_current() currently open codes task_css() and
css_tryget_online() to find and pin $current's blkcg css. Abstract it
into task_get_css() which is implemented from cgroup side. As a task
is always associated with an online css for every subsystem except
while the css_set update is propagating, task_get_css() retries till
css_tryget_online() succeeds.
This is a cleanup and shouldn't lead to noticeable behavior changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Vivek Goyal <vgoyal@redhat.com>
---
block/bio.c | 11 +----------
include/linux/cgroup.h | 25 +++++++++++++++++++++++++
2 files changed, 26 insertions(+), 10 deletions(-)
diff --git a/block/bio.c b/block/bio.c
index f66a4ea..968683e 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1987,7 +1987,6 @@ EXPORT_SYMBOL(bioset_create_nobvec);
int bio_associate_current(struct bio *bio)
{
struct io_context *ioc;
- struct cgroup_subsys_state *css;
if (bio->bi_ioc)
return -EBUSY;
@@ -1996,17 +1995,9 @@ int bio_associate_current(struct bio *bio)
if (!ioc)
return -ENOENT;
- /* acquire active ref on @ioc and associate */
get_io_context_active(ioc);
bio->bi_ioc = ioc;
-
- /* associate blkcg if exists */
- rcu_read_lock();
- css = task_css(current, blkio_cgrp_id);
- if (css && css_tryget_online(css))
- bio->bi_css = css;
- rcu_read_unlock();
-
+ bio->bi_css = task_get_css(current, blkio_cgrp_id);
return 0;
}
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index b9cb94c..e7da0aa 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -774,6 +774,31 @@ static inline struct cgroup_subsys_state *task_css(struct task_struct *task,
}
/**
+ * task_get_css - find and get the css for (task, subsys)
+ * @task: the target task
+ * @subsys_id: the target subsystem ID
+ *
+ * Find the css for the (@task, @subsys_id) combination, increment a
+ * reference on and return it. This function is guaranteed to return a
+ * valid css.
+ */
+static inline struct cgroup_subsys_state *
+task_get_css(struct task_struct *task, int subsys_id)
+{
+ struct cgroup_subsys_state *css;
+
+ rcu_read_lock();
+ while (true) {
+ css = task_css(task, subsys_id);
+ if (likely(css_tryget_online(css)))
+ break;
+ cpu_relax();
+ }
+ rcu_read_unlock();
+ return css;
+}
+
+/**
* task_css_is_root - test whether a task belongs to the root css
* @task: the target task
* @subsys_id: the target subsystem ID
--
2.4.1
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v11 5/7] cgroup: move enum cgroup_subsys_id definition
2015-05-16 4:13 [PATCH v11 0/7] cgroups: add pids subsystem Aleksa Sarai
` (3 preceding siblings ...)
2015-05-16 4:13 ` [PATCH v11 4/7] cgroup, block: implement task_get_css() and use it in bio_associate_current() Aleksa Sarai
@ 2015-05-16 4:13 ` Aleksa Sarai
2015-05-16 4:13 ` [PATCH v11 6/7] cgroup: allow a cgroup subsystem to reject a fork Aleksa Sarai
2015-05-16 4:13 ` [PATCH v11 7/7] cgroup: implement the PIDs subsystem Aleksa Sarai
6 siblings, 0 replies; 11+ messages in thread
From: Aleksa Sarai @ 2015-05-16 4:13 UTC (permalink / raw)
To: tj, lizefan, mingo, peterz
Cc: richard, fweisbec, linux-kernel, cgroups, Aleksa Sarai
This patch is in preparation for the pids cgroup subsystem patchset.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
include/linux/cgroup.h | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index e7da0aa..35ba593 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -25,6 +25,14 @@
#ifdef CONFIG_CGROUPS
+/* define the enumeration of all cgroup subsystems */
+#define SUBSYS(_x) _x ## _cgrp_id,
+enum cgroup_subsys_id {
+#include <linux/cgroup_subsys.h>
+ CGROUP_SUBSYS_COUNT,
+};
+#undef SUBSYS
+
struct cgroup_root;
struct cgroup_subsys;
struct cgroup;
@@ -40,14 +48,6 @@ extern int cgroupstats_build(struct cgroupstats *stats,
extern int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *tsk);
-/* define the enumeration of all cgroup subsystems */
-#define SUBSYS(_x) _x ## _cgrp_id,
-enum cgroup_subsys_id {
-#include <linux/cgroup_subsys.h>
- CGROUP_SUBSYS_COUNT,
-};
-#undef SUBSYS
-
/*
* Per-subsystem/per-cgroup state maintained by the system. This is the
* fundamental structural building block that controllers deal with.
--
2.4.1
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v11 6/7] cgroup: allow a cgroup subsystem to reject a fork
2015-05-16 4:13 [PATCH v11 0/7] cgroups: add pids subsystem Aleksa Sarai
` (4 preceding siblings ...)
2015-05-16 4:13 ` [PATCH v11 5/7] cgroup: move enum cgroup_subsys_id definition Aleksa Sarai
@ 2015-05-16 4:13 ` Aleksa Sarai
2015-05-16 4:13 ` [PATCH v11 7/7] cgroup: implement the PIDs subsystem Aleksa Sarai
6 siblings, 0 replies; 11+ messages in thread
From: Aleksa Sarai @ 2015-05-16 4:13 UTC (permalink / raw)
To: tj, lizefan, mingo, peterz
Cc: richard, fweisbec, linux-kernel, cgroups, Aleksa Sarai
Add a new cgroup subsystem callback can_fork that conditionally
states whether or not the fork is accepted or rejected by a cgroup
policy. In addition, add a cancel_fork callback so that if an error
occurs later in the forking process, any state modified by can_fork can
be reverted.
Allow for a private opaque pointer to be passed from the cgroup_can_fork
to cgroup_post_fork, allowing for the fork state to be stored by each
subsystem separately.
In order for a subsystem to know that a task associated with a cgroup
hierarchy is being migrated to another hierarchy, add a detach callback
to the subsystem which is run after the migration has been confirmed but
before the old_cset's refcount is dropped. This is necessary in order
for a subsystem to be able to keep a proper count of how many tasks are
associated with that subsystem.
Also add a tagging system for cgroup_subsys.h to allow for CGROUP_<TAG>
enumerations to be be defined and used (as well as CGROUP_<TAG>_COUNT).
This is in preparation for implementing the pids cgroup subsystem.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
include/linux/cgroup.h | 35 +++++++++++++++--
include/linux/cgroup_subsys.h | 17 ++++++++
kernel/cgroup.c | 90 +++++++++++++++++++++++++++++++++++++++----
kernel/cgroup_freezer.c | 2 +-
kernel/fork.c | 17 +++++++-
kernel/sched/core.c | 2 +-
6 files changed, 149 insertions(+), 14 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 35ba593..ef9d21c 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -28,11 +28,16 @@
/* define the enumeration of all cgroup subsystems */
#define SUBSYS(_x) _x ## _cgrp_id,
enum cgroup_subsys_id {
+#define SUBSYS_TAG(_t) CGROUP_ ## _t, \
+ __unused_tag_ ## _t = CGROUP_ ## _t - 1,
#include <linux/cgroup_subsys.h>
+#undef SUBSYS_TAG
CGROUP_SUBSYS_COUNT,
};
#undef SUBSYS
+#define CGROUP_CANFORK_COUNT (CGROUP_CANFORK_END - CGROUP_CANFORK_START)
+
struct cgroup_root;
struct cgroup_subsys;
struct cgroup;
@@ -40,7 +45,12 @@ struct cgroup;
extern int cgroup_init_early(void);
extern int cgroup_init(void);
extern void cgroup_fork(struct task_struct *p);
-extern void cgroup_post_fork(struct task_struct *p);
+extern int cgroup_can_fork(struct task_struct *p,
+ void *ss_private[CGROUP_CANFORK_COUNT]);
+extern void cgroup_cancel_fork(struct task_struct *p,
+ void *ss_private[CGROUP_CANFORK_COUNT]);
+extern void cgroup_post_fork(struct task_struct *p,
+ void *old_ss_private[CGROUP_CANFORK_COUNT]);
extern void cgroup_exit(struct task_struct *p);
extern int cgroupstats_build(struct cgroupstats *stats,
struct dentry *dentry);
@@ -629,6 +639,14 @@ struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset);
for ((task) = cgroup_taskset_first((tset)); (task); \
(task) = cgroup_taskset_next((tset)))
+/**
+ * tset_get_css - obtain and get css for (tset, subsys_id)
+ * @tset: target taskset
+ * @subsys_id: target subsystem id
+ */
+#define tset_get_css(tset, subsys_id) \
+ task_get_css(cgroup_taskset_first(tset), subsys_id)
+
/*
* Control Group subsystem type.
* See Documentation/cgroups/cgroups.txt for details
@@ -649,7 +667,9 @@ struct cgroup_subsys {
struct cgroup_taskset *tset);
void (*attach)(struct cgroup_subsys_state *css,
struct cgroup_taskset *tset);
- void (*fork)(struct task_struct *task);
+ int (*can_fork)(struct task_struct *task, void **privatep);
+ void (*cancel_fork)(struct task_struct *task, void *private);
+ void (*fork)(struct task_struct *task, void *private);
void (*exit)(struct cgroup_subsys_state *css,
struct cgroup_subsys_state *old_css,
struct task_struct *task);
@@ -970,10 +990,19 @@ struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
struct cgroup_subsys_state;
+#define CGROUP_CANFORK_COUNT 0
+
static inline int cgroup_init_early(void) { return 0; }
static inline int cgroup_init(void) { return 0; }
static inline void cgroup_fork(struct task_struct *p) {}
-static inline void cgroup_post_fork(struct task_struct *p) {}
+static inline int cgroup_can_fork(struct task_struct *p,
+ void *ss_private[CGROUP_CANFORK_COUNT])
+{ return 0; }
+static inline void cgroup_cancel_fork(struct task_struct *p,
+ void *ss_private[CGROUP_CANFORK_COUNT]) {}
+static inline void cgroup_post_fork(struct task_struct *p,
+ void *ss_private[CGROUP_CANFORK_COUNT]) {}
+
static inline void cgroup_exit(struct task_struct *p) {}
static inline int cgroupstats_build(struct cgroupstats *stats,
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index e4a96fb..81b7bdd 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -3,6 +3,11 @@
*
* DO NOT ADD ANY SUBSYSTEM WITHOUT EXPLICIT ACKS FROM CGROUP MAINTAINERS.
*/
+#ifndef SUBSYS_TAG
+# define __TMP_SUBSYS_TAG
+# define SUBSYS_TAG(_x)
+#endif
+
#if IS_ENABLED(CONFIG_CPUSETS)
SUBSYS(cpuset)
#endif
@@ -48,11 +53,23 @@ SUBSYS(hugetlb)
#endif
/*
+ * Subsystems that implement the can_fork() family of callbacks.
+ */
+SUBSYS_TAG(CANFORK_START)
+SUBSYS_TAG(CANFORK_END)
+
+/*
* The following subsystems are not supported on the default hierarchy.
*/
#if IS_ENABLED(CONFIG_CGROUP_DEBUG)
SUBSYS(debug)
#endif
+
+#ifdef __TMP_SUBSYS_TAG
+# undef __TMP_SUBSYS_TAG
+# undef SUBSYS_TAG
+#endif
+
/*
* DO NOT ADD ANY SUBSYSTEM WITHOUT EXPLICIT ACKS FROM CGROUP MAINTAINERS.
*/
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index eb5e4b3..c3dfcc2 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -176,14 +176,17 @@ static DEFINE_IDR(cgroup_hierarchy_idr);
static u64 css_serial_nr_next = 1;
/*
- * These bitmask flags indicate whether tasks in the fork and exit paths should
- * check for fork/exit handlers to call. This avoids us having to do
- * extra work in the fork/exit path if none of the subsystems need to
- * be called.
+ * These bitmask flags indicate whether tasks in the fork and exit paths
+ * should check for fork/exit handlers to call. This avoids us having to do
+ * extra work in the fork/exit path if a subsystems doesn't need to be
+ * called.
*/
static unsigned long have_fork_callback __read_mostly;
static unsigned long have_exit_callback __read_mostly;
+/* Ditto for the can_fork callback. */
+static unsigned long have_canfork_callback __read_mostly;
+
static struct cftype cgroup_dfl_base_files[];
static struct cftype cgroup_legacy_base_files[];
@@ -2325,9 +2328,10 @@ static int cgroup_migrate(struct cgroup *cgrp, struct task_struct *leader,
*/
tset.csets = &tset.dst_csets;
- for_each_e_css(css, i, cgrp)
+ for_each_e_css(css, i, cgrp) {
if (css->ss->attach)
css->ss->attach(css, &tset);
+ }
ret = 0;
goto out_release_tset;
@@ -4940,6 +4944,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
have_fork_callback |= (bool)ss->fork << ss->id;
have_exit_callback |= (bool)ss->exit << ss->id;
+ have_canfork_callback |= (bool)ss->can_fork << ss->id;
/* At system boot, before all subsystems have been
* registered, no tasks have been forked, so we don't
@@ -5181,6 +5186,21 @@ static const struct file_operations proc_cgroupstats_operations = {
.release = single_release,
};
+static void **subsys_canfork_privatep(void *ss_private[], int i)
+{
+ if (CGROUP_CANFORK_START <= i && i < CGROUP_CANFORK_END)
+ return &ss_private[i - CGROUP_CANFORK_START];
+ return NULL;
+}
+
+static void *subsys_canfork_private(void *ss_private[], int i)
+{
+ void **private;
+ if ((private = subsys_canfork_privatep(ss_private, i)) != NULL)
+ return *private;
+ return NULL;
+}
+
/**
* cgroup_fork - initialize cgroup related fields during copy_process()
* @child: pointer to task_struct of forking parent process.
@@ -5196,6 +5216,61 @@ void cgroup_fork(struct task_struct *child)
}
/**
+ * cgroup_can_fork - called on a new task before the process is exposed
+ * @child: the task in question.
+ *
+ * This calls the subsystem can_fork() callbacks. If the can_fork() callback
+ * returns an error, the fork aborts with that error code. This allows for
+ * a cgroup subsystem to conditionally allow or deny new forks.
+ */
+int cgroup_can_fork(struct task_struct *child,
+ void *ss_private[CGROUP_CANFORK_COUNT])
+{
+ struct cgroup_subsys *ss;
+ int i, j, retval;
+
+ for_each_subsys_which(ss, i, &have_canfork_callback) {
+ retval = ss->can_fork(child,
+ subsys_canfork_privatep(ss_private, i));
+ if (retval)
+ goto out_revert;
+ }
+
+ return 0;
+
+out_revert:
+ for_each_subsys(ss, j) {
+ if (j >= i)
+ break;
+
+ if (ss->cancel_fork)
+ ss->cancel_fork(child,
+ subsys_canfork_private(ss_private, j));
+ }
+
+ return retval;
+}
+
+/**
+ * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
+ * @child: the task in question
+ *
+ * This calls the cancel_fork() callbacks if a fork failed *after*
+ * cgroup_can_fork() succeded.
+ */
+void cgroup_cancel_fork(struct task_struct *child,
+ void *ss_private[CGROUP_CANFORK_COUNT])
+{
+ struct cgroup_subsys *ss;
+ int i;
+
+ for_each_subsys(ss, i)
+ if(ss->cancel_fork)
+ ss->cancel_fork(child,
+ subsys_canfork_private(ss_private, i));
+}
+
+/**
* cgroup_post_fork - called on a new task after adding it to the task list
* @child: the task in question
*
@@ -5205,7 +5280,8 @@ void cgroup_fork(struct task_struct *child)
* cgroup_task_iter_start() - to guarantee that the new task ends up on its
* list.
*/
-void cgroup_post_fork(struct task_struct *child)
+void cgroup_post_fork(struct task_struct *child,
+ void *old_ss_private[CGROUP_CANFORK_COUNT])
{
struct cgroup_subsys *ss;
int i;
@@ -5250,7 +5326,7 @@ void cgroup_post_fork(struct task_struct *child)
* and addition to css_set.
*/
for_each_subsys_which(ss, i, &have_fork_callback)
- ss->fork(child);
+ ss->fork(child, subsys_canfork_private(old_ss_private, i));
}
/**
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 92b98cc..f1b30ad 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -203,7 +203,7 @@ static void freezer_attach(struct cgroup_subsys_state *new_css,
* to do anything as freezer_attach() will put @task into the appropriate
* state.
*/
-static void freezer_fork(struct task_struct *task)
+static void freezer_fork(struct task_struct *task, void *private)
{
struct freezer *freezer;
diff --git a/kernel/fork.c b/kernel/fork.c
index 03c1eaa..7377698 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1245,6 +1245,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
{
int retval;
struct task_struct *p;
+ void *cgrp_ss_private[CGROUP_CANFORK_COUNT] = {};
if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
return ERR_PTR(-EINVAL);
@@ -1516,6 +1517,16 @@ static struct task_struct *copy_process(unsigned long clone_flags,
p->task_works = NULL;
/*
+ * Ensure that the cgroup subsystem policies allow the new process to be
+ * forked. It should be noted the the new process's css_set can be changed
+ * between here and cgroup_post_fork() if an organisation operation is in
+ * progress.
+ */
+ retval = cgroup_can_fork(p, cgrp_ss_private);
+ if (retval)
+ goto bad_fork_free_pid;
+
+ /*
* Make it visible to the rest of the system, but dont wake it up yet.
* Need tasklist lock for parent etc handling!
*/
@@ -1551,7 +1562,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
spin_unlock(¤t->sighand->siglock);
write_unlock_irq(&tasklist_lock);
retval = -ERESTARTNOINTR;
- goto bad_fork_free_pid;
+ goto bad_fork_cancel_cgroup;
}
if (likely(p->pid)) {
@@ -1593,7 +1604,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
write_unlock_irq(&tasklist_lock);
proc_fork_connector(p);
- cgroup_post_fork(p);
+ cgroup_post_fork(p, cgrp_ss_private);
if (clone_flags & CLONE_THREAD)
threadgroup_change_end(current);
perf_event_fork(p);
@@ -1603,6 +1614,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
return p;
+bad_fork_cancel_cgroup:
+ cgroup_cancel_fork(p, cgrp_ss_private);
bad_fork_free_pid:
if (pid != &init_struct_pid)
free_pid(pid);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f9123a8..050936e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8007,7 +8007,7 @@ static void cpu_cgroup_css_offline(struct cgroup_subsys_state *css)
sched_offline_group(tg);
}
-static void cpu_cgroup_fork(struct task_struct *task)
+static void cpu_cgroup_fork(struct task_struct *task, void *private)
{
sched_move_task(task);
}
--
2.4.1
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v11 7/7] cgroup: implement the PIDs subsystem
2015-05-16 4:13 [PATCH v11 0/7] cgroups: add pids subsystem Aleksa Sarai
` (5 preceding siblings ...)
2015-05-16 4:13 ` [PATCH v11 6/7] cgroup: allow a cgroup subsystem to reject a fork Aleksa Sarai
@ 2015-05-16 4:13 ` Aleksa Sarai
2015-05-18 13:16 ` Aleksa Sarai
2015-06-05 19:57 ` Aleksa Sarai
6 siblings, 2 replies; 11+ messages in thread
From: Aleksa Sarai @ 2015-05-16 4:13 UTC (permalink / raw)
To: tj, lizefan, mingo, peterz
Cc: richard, fweisbec, linux-kernel, cgroups, Aleksa Sarai
Adds a new single-purpose PIDs subsystem to limit the number of
tasks that can be forked inside a cgroup. Essentially this is an
implementation of RLIMIT_NPROC that applies to a cgroup rather than a
process tree.
However, it should be noted that organisational operations (adding and
removing tasks from a PIDs hierarchy) will *not* be prevented. Rather,
the number of tasks in the hierarchy cannot exceed the limit through
forking. This is due to the fact that, in the unified hierarchy, attach
cannot fail (and it is not possible for a task to overcome its PIDs
cgroup policy limit by attaching to a child cgroup).
PIDs are fundamentally a global resource, and it is possible to reach
PID exhaustion inside a cgroup without hitting any reasonable kmemcg
policy. Once you've hit PID exhaustion, you're only in a marginally
better state than OOM. This subsystem allows PID exhaustion inside a
cgroup to be prevented.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
CREDITS | 5 +
include/linux/cgroup_subsys.h | 5 +
init/Kconfig | 16 ++
kernel/Makefile | 1 +
kernel/cgroup_pids.c | 379 ++++++++++++++++++++++++++++++++++++++++++
5 files changed, 406 insertions(+)
create mode 100644 kernel/cgroup_pids.c
diff --git a/CREDITS b/CREDITS
index 40cc4bf..0727426 100644
--- a/CREDITS
+++ b/CREDITS
@@ -3215,6 +3215,11 @@ S: 69 rue Dunois
S: 75013 Paris
S: France
+N: Aleksa Sarai
+E: cyphar@cyphar.com
+W: https://www.cyphar.com/
+D: `pids` cgroup subsystem
+
N: Dipankar Sarma
E: dipankar@in.ibm.com
D: RCU
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index 81b7bdd..32becaf 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -56,6 +56,11 @@ SUBSYS(hugetlb)
* Subsystems that implement the can_fork() family of callbacks.
*/
SUBSYS_TAG(CANFORK_START)
+
+#if IS_ENABLED(CONFIG_CGROUP_PIDS)
+SUBSYS(pids)
+#endif
+
SUBSYS_TAG(CANFORK_END)
/*
diff --git a/init/Kconfig b/init/Kconfig
index dc24dec..24b2563 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -967,6 +967,22 @@ config CGROUP_FREEZER
Provides a way to freeze and unfreeze all tasks in a
cgroup.
+config CGROUP_PIDS
+ bool "PIDs cgroup subsystem"
+ help
+ Provides enforcement of process number limits in the scope of a
+ cgroup. Any attempt to fork more processes than is allowed in the
+ cgroup will fail. PIDs are fundamentally a global resource because it
+ is fairly trivial to reach PID exhaustion before you reach even a
+ conservative kmemcg limit. As a result, it is possible to grind a
+ system to halt without being limited by other cgroup policies. The
+ PIDs cgroup subsystem is designed to stop this from happening.
+
+ It should be noted that organisational operations (such as attaching
+ to a cgroup hierarchy will *not* be blocked by the PIDs subsystem),
+ since the PIDs limit only affects a process's ability to fork, not to
+ attach to a cgroup.
+
config CGROUP_DEVICE
bool "Device controller for cgroups"
help
diff --git a/kernel/Makefile b/kernel/Makefile
index 0f8f8b0..df5406c 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -55,6 +55,7 @@ obj-$(CONFIG_BACKTRACE_SELF_TEST) += backtracetest.o
obj-$(CONFIG_COMPAT) += compat.o
obj-$(CONFIG_CGROUPS) += cgroup.o
obj-$(CONFIG_CGROUP_FREEZER) += cgroup_freezer.o
+obj-$(CONFIG_CGROUP_PIDS) += cgroup_pids.o
obj-$(CONFIG_CPUSETS) += cpuset.o
obj-$(CONFIG_UTS_NS) += utsname.o
obj-$(CONFIG_USER_NS) += user_namespace.o
diff --git a/kernel/cgroup_pids.c b/kernel/cgroup_pids.c
new file mode 100644
index 0000000..8457da6
--- /dev/null
+++ b/kernel/cgroup_pids.c
@@ -0,0 +1,379 @@
+/*
+ * Process number limiting controller for cgroups.
+ *
+ * Used to allow a cgroup hierarchy to stop any new processes from fork()ing
+ * after a certain limit is reached.
+ *
+ * Since it is trivial to hit the task limit without hitting any kmemcg limits
+ * in place, PIDs are a fundamental resource. As such, PID exhaustion must be
+ * preventable in the scope of a cgroup hierarchy by allowing resource limiting
+ * of the number of tasks in a cgroup.
+ *
+ * In order to use the `pids` controller, set the maximum number of tasks in
+ * pids.max (this is not available in the root cgroup for obvious reasons). The
+ * number of processes currently in the cgroup is given by pids.current.
+ * Organisational operations are not blocked by cgroup policies, so it is
+ * possible to have pids.current > pids.max. However, it is not possible to
+ * violate a cgroup policy through fork(). fork() will retrun -EAGAIN if forking
+ * would cause a cgroup policy to be violated.
+ *
+ * To set a cgroup to have no limit, set pids.max to "max". This is the default
+ * for all new cgroups (NB that PID limits are hierarchical, so the most
+ * stringent limit in the hierarchy is followed).
+ *
+ * pids.current tracks all child cgroup hierarchies, so parent/pids.current is
+ * a superset of parent/child/pids.current.
+ *
+ * Copyright (C) 2015 Aleksa Sarai <cyphar@cyphar.com>
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/threads.h>
+#include <linux/atomic.h>
+#include <linux/cgroup.h>
+#include <linux/slab.h>
+
+#define PIDS_MAX (PID_MAX_LIMIT + 1ULL)
+#define PIDS_MAX_STR "max"
+
+struct pids_cgroup {
+ struct cgroup_subsys_state css;
+
+ /*
+ * Use 64-bit types so that we can safely represent "max" as
+ * %PIDS_MAX = (%PID_MAX_LIMIT + 1).
+ */
+ atomic64_t counter;
+ int64_t limit;
+};
+
+static struct pids_cgroup *css_pids(struct cgroup_subsys_state *css)
+{
+ return container_of(css, struct pids_cgroup, css);
+}
+/*
+static struct pids_cgroup *task_pids(struct task_struct *task)
+{
+ return css_pids(task_css(task));
+}
+*/
+
+static struct pids_cgroup *parent_pids(struct pids_cgroup *pids)
+{
+ return css_pids(pids->css.parent);
+}
+
+static struct cgroup_subsys_state *
+pids_css_alloc(struct cgroup_subsys_state *parent)
+{
+ struct pids_cgroup *pids;
+
+ pids = kzalloc(sizeof(struct pids_cgroup), GFP_KERNEL);
+ if (!pids)
+ return ERR_PTR(-ENOMEM);
+
+ pids->limit = PIDS_MAX;
+ atomic64_set(&pids->counter, 0);
+ return &pids->css;
+}
+
+static void pids_css_free(struct cgroup_subsys_state *css)
+{
+ kfree(css_pids(css));
+}
+
+/**
+ * pids_cancel - uncharge the local pid count
+ * @pids: the pid cgroup state
+ * @num: the number of pids to cancel
+ *
+ * This function will WARN if the pid count goes under 0, because such a case is
+ * a bug in the pids controller proper.
+ */
+static void pids_cancel(struct pids_cgroup *pids, int num)
+{
+ /*
+ * A negative count (or overflow for that matter) is invalid,
+ * and indicates a bug in the pids controller proper.
+ */
+ WARN_ON_ONCE(atomic64_add_negative(-num, &pids->counter));
+}
+
+/**
+ * pids_uncharge - hierarchically uncharge the pid count
+ * @pids: the pid cgroup state
+ * @num: the number of pids to uncharge
+ */
+static void pids_uncharge(struct pids_cgroup *pids, int num)
+{
+ struct pids_cgroup *p;
+
+ for (p = pids; p; p = parent_pids(p))
+ pids_cancel(p, num);
+}
+
+/**
+ * pids_charge - hierarchically charge the pid count
+ * @pids: the pid cgroup state
+ * @num: the number of pids to charge
+ *
+ * This function does *not* follow the pid limit set. It cannot fail and the new
+ * pid count may exceed the limit, because organisational operations cannot fail
+ * in the unified hierarchy.
+ */
+static void pids_charge(struct pids_cgroup *pids, int num)
+{
+ struct pids_cgroup *p;
+
+ for (p = pids; p; p = parent_pids(p))
+ atomic64_add(num, &p->counter);
+}
+
+/**
+ * pids_try_charge - hierarchically try to charge the pid count
+ * @pids: the pid cgroup state
+ * @num: the number of pids to charge
+ *
+ * This function follows the set limit. It will fail if the charge would cause
+ * the new value to exceed the hierarchical limit. Returns 0 if the charge
+ * succeded, otherwise -EAGAIN.
+ */
+static int pids_try_charge(struct pids_cgroup *pids, int num)
+{
+ struct pids_cgroup *p, *q;
+
+ for (p = pids; p; p = parent_pids(p)) {
+ int64_t new = atomic64_add_return(num, &p->counter);
+
+ /*
+ * Since new is capped to the maximum number of pid_t, if
+ * p->limit is %PIDS_MAX then we know that this test will never
+ * fail.
+ */
+ if (new > p->limit)
+ goto revert;
+ }
+
+ return 0;
+
+revert:
+ for (q = pids; q != p; q = parent_pids(q))
+ pids_cancel(q, num);
+ pids_cancel(p, num);
+
+ return -EAGAIN;
+}
+
+static int pids_can_attach(struct cgroup_subsys_state *css,
+ struct cgroup_taskset *tset)
+{
+ struct pids_cgroup *pids = css_pids(css);
+ struct cgroup_subsys_state *old_css;
+ struct pids_cgroup *old_pids;
+ struct task_struct *task;
+ int64_t num = 0;
+
+ /*
+ * We are guaranteed that all tasks in the tset have the same css, so
+ * we only need to get one ref to it.
+ */
+ old_css = tset_get_css(tset, pids_cgrp_id);
+ old_pids = css_pids(old_css);
+
+ cgroup_taskset_for_each(task, tset)
+ num++;
+
+ /*
+ * Attaching to a cgroup is allowed to overcome the
+ * the PID limit, so that organisation operations aren't
+ * blocked by the `pids` cgroup controller.
+ */
+ pids_charge(pids, num);
+ pids_uncharge(old_pids, num);
+ css_put(old_css);
+ return 0;
+}
+
+static void pids_cancel_attach(struct cgroup_subsys_state *css,
+ struct cgroup_taskset *tset)
+{
+ struct pids_cgroup *pids = css_pids(css);
+ struct cgroup_subsys_state *old_css;
+ struct pids_cgroup *old_pids;
+ struct task_struct *task;
+ int64_t num = 0;
+
+ /*
+ * We are guaranteed that all tasks in the tset have the same css, so
+ * we only need to get one ref to it.
+ */
+ old_css = tset_get_css(tset, pids_cgrp_id);
+ old_pids = css_pids(old_css);
+
+ cgroup_taskset_for_each(task, tset)
+ num++;
+
+ pids_charge(old_pids, num);
+ pids_uncharge(pids, num);
+ css_put(old_css);
+}
+
+static int pids_can_fork(struct task_struct *task, void **private)
+{
+ struct cgroup_subsys_state *css;
+ struct pids_cgroup *pids;
+ int retval;
+
+ /*
+ * Use the "current" task_css for the pids subsystem as the tentative
+ * css. It is possible we will charge the wrong hierarchy, in which
+ * case we will forcefully revert/reapply the charge on the right
+ * hierarchy after it is committed to the task proper.
+ */
+ css = task_get_css(current, pids_cgrp_id);
+ pids = css_pids(css);
+
+ retval = pids_try_charge(pids, 1);
+ if (retval)
+ goto err_css_put;
+
+ *private = css;
+ return 0;
+
+err_css_put:
+ css_put(css);
+ return retval;
+}
+
+static void pids_cancel_fork(struct task_struct *task, void *private)
+{
+ struct cgroup_subsys_state *css = private;
+ struct pids_cgroup *pids = css_pids(css);
+
+ pids_uncharge(pids, 1);
+ css_put(css);
+}
+
+static void pids_fork(struct task_struct *task, void *private)
+{
+ struct cgroup_subsys_state *css;
+ struct cgroup_subsys_state *old_css = private;
+ struct pids_cgroup *pids;
+ struct pids_cgroup *old_pids = css_pids(old_css);
+
+ /*
+ * Get the task's css after it has been committed proper. Since this
+ * task has already been exposed to the system, there's an implicit
+ * implicit reference to the task's css. But grab a ref anyway.
+ */
+ css = task_get_css(task, pids_cgrp_id);
+ pids = css_pids(css);
+
+ /*
+ * If the association has changed, we have to revert and reapply the
+ * charge/uncharge on the wrong hierarchy to the current one. Since
+ * the association can only change due to an organisation event, its
+ * okay for us to ignore the limit in this case.
+ */
+ if (pids != old_pids) {
+ pids_uncharge(old_pids, 1);
+ pids_charge(pids, 1);
+ }
+
+ css_put(css);
+ css_put(old_css);
+}
+
+static void pids_exit(struct cgroup_subsys_state *css,
+ struct cgroup_subsys_state *old_css,
+ struct task_struct *task)
+{
+ /*
+ * We use @old_css here, because the task has reassigned to init_css_set
+ * at this point (it's weird that you even get @css passed, because it's
+ * always going to be init_css_set).
+ */
+ struct pids_cgroup *pids = css_pids(old_css);
+
+ pids_uncharge(pids, 1);
+}
+
+static ssize_t pids_max_write(struct kernfs_open_file *of, char *buf,
+ size_t nbytes, loff_t off)
+{
+ struct cgroup_subsys_state *css = of_css(of);
+ struct pids_cgroup *pids = css_pids(css);
+ int64_t limit;
+ int err;
+
+ buf = strstrip(buf);
+ if (!strcmp(buf, PIDS_MAX_STR)) {
+ limit = PIDS_MAX;
+ goto set_limit;
+ }
+
+ err = kstrtoll(buf, 0, &limit);
+ if (err)
+ return err;
+
+ if (limit < 0 || limit >= PIDS_MAX)
+ return -EINVAL;
+
+set_limit:
+ /*
+ * Limit updates don't need to be mutex'd, since it isn't
+ * critical that any racing fork()s follow the new limit.
+ */
+ pids->limit = limit;
+ return nbytes;
+}
+
+static int pids_max_show(struct seq_file *sf, void *v)
+{
+ struct cgroup_subsys_state *css = seq_css(sf);
+ struct pids_cgroup *pids = css_pids(css);
+ int64_t limit = pids->limit;
+
+ if (limit >= PIDS_MAX)
+ seq_printf(sf, "%s\n", PIDS_MAX_STR);
+ else
+ seq_printf(sf, "%lld\n", limit);
+
+ return 0;
+}
+
+static s64 pids_current_read(struct cgroup_subsys_state *css,
+ struct cftype *cft)
+{
+ struct pids_cgroup *pids = css_pids(css);
+
+ return atomic64_read(&pids->counter);
+}
+
+static struct cftype files[] = {
+ {
+ .name = "max",
+ .write = pids_max_write,
+ .seq_show = pids_max_show,
+ .flags = CFTYPE_NOT_ON_ROOT,
+ },
+ {
+ .name = "current",
+ .read_s64 = pids_current_read,
+ },
+ { } /* terminate */
+};
+
+struct cgroup_subsys pids_cgrp_subsys = {
+ .css_alloc = pids_css_alloc,
+ .css_free = pids_css_free,
+ .can_attach = pids_can_attach,
+ .cancel_attach = pids_cancel_attach,
+ .can_fork = pids_can_fork,
+ .cancel_fork = pids_cancel_fork,
+ .fork = pids_fork,
+ .exit = pids_exit,
+ .legacy_cftypes = files,
+ .early_init = 0,
+};
--
2.4.1
^ permalink raw reply [flat|nested] 11+ messages in thread* Re: [PATCH v11 7/7] cgroup: implement the PIDs subsystem
2015-05-16 4:13 ` [PATCH v11 7/7] cgroup: implement the PIDs subsystem Aleksa Sarai
@ 2015-05-18 13:16 ` Aleksa Sarai
2015-06-05 19:57 ` Aleksa Sarai
1 sibling, 0 replies; 11+ messages in thread
From: Aleksa Sarai @ 2015-05-18 13:16 UTC (permalink / raw)
To: Tejun Heo, lizefan, mingo, Peter Zijlstra
Cc: richard, Frédéric Weisbecker, linux-kernel, cgroups,
Aleksa Sarai
I just realised I didn't remove a few incorrect comments and some of
the other patches need a small amount of fixing up. I'll send a
corrected patchset in an hour or so.
--
Aleksa Sarai (cyphar)
www.cyphar.com
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v11 7/7] cgroup: implement the PIDs subsystem
2015-05-16 4:13 ` [PATCH v11 7/7] cgroup: implement the PIDs subsystem Aleksa Sarai
2015-05-18 13:16 ` Aleksa Sarai
@ 2015-06-05 19:57 ` Aleksa Sarai
2015-06-05 20:05 ` Aleksa Sarai
1 sibling, 1 reply; 11+ messages in thread
From: Aleksa Sarai @ 2015-06-05 19:57 UTC (permalink / raw)
To: Tejun Heo
Cc: lizefan, mingo, Peter Zijlstra, richard,
Frédéric Weisbecker, linux-kernel, cgroups,
Aleksa Sarai
Hello Tejun,
Is it safe for us to task_get_css() every task in the tset in
->can_attach() and then put_css() in ->attach() and ->cancel_attach()?
In other words: if we have a ref to a task's css, are we guaranteed
that the task_css() will return the same thing every time? Here's what
I'm currently doing:
static int pids_can_attach(struct cgroup_subsys_state *css,
struct cgroup_taskset *tset)
{
struct pids_cgroup *pids = css_pids(css);
struct task_struct *task, *fail_task;
int err;
cgroup_taskset_for_each(task, tset) {
struct cgroup_subsys_state *old_css;
struct pids_cgroup *old_pids;
old_css = task_get_css(task, pids_cgrp_id);
old_pids = css_pids(old_css);
err = pids_try_charge(pids, 1);
if (err)
goto out_fail;
pids_uncharge(old_pids, 1);
continue;
out_fail:
fail_task = task;
goto err_revert;
}
return 0;
err_revert:
cgroup_taskset_for_each(task, tset) {
css_put(task_css(task, pids_cgrp_id));
if (task == fail_task)
break;
pids_uncharge(pids, 1);
}
return err;
}
static void pids_cancel_attach(struct cgroup_subsys_state *css,
struct cgroup_taskset *tset)
{
struct pids_cgroup *pids = css_pids(css);
struct task_struct *task;
cgroup_taskset_for_each(task, tset) {
struct cgroup_subsys_state *old_css;
struct pids_cgroup *old_pids;
old_css = task_css(task, pids_cgrp_id);
old_pids = css_pids(old_css);
pids_charge(old_pids, 1);
pids_uncharge(pids, 1);
css_put(old_css);
}
}
static void pids_attach(struct cgroup_subsys_state *css,
struct cgroup_taskset *tset)
{
struct task_struct *task;
cgroup_taskset_for_each(task, tset)
css_put(task_css(task, pids_cgrp_id));
}
--
Aleksa Sarai (cyphar)
www.cyphar.com
^ permalink raw reply [flat|nested] 11+ messages in thread* Re: [PATCH v11 7/7] cgroup: implement the PIDs subsystem
2015-06-05 19:57 ` Aleksa Sarai
@ 2015-06-05 20:05 ` Aleksa Sarai
0 siblings, 0 replies; 11+ messages in thread
From: Aleksa Sarai @ 2015-06-05 20:05 UTC (permalink / raw)
To: Tejun Heo
Cc: lizefan, mingo, Peter Zijlstra, richard,
Frédéric Weisbecker, linux-kernel, cgroups,
Aleksa Sarai
> err = pids_try_charge(pids, 1);
> if (err)
> goto out_fail;
Disregard this and the revert code. This was from me testing making
attach obey the set limit (which isn't going to in to the patchset).
--
Aleksa Sarai (cyphar)
www.cyphar.com
^ permalink raw reply [flat|nested] 11+ messages in thread