[PATCH v2 1/2] proc: add tgid_iter.pid_ns member

[PATCH v2 1/2] proc: add tgid_iter.pid_ns member

[Alexey Dobriyan]

next_tgid() accept pid namespace as an argument, but it is never changes
during readdir (which would be unthinkable thing to do anyway).

Move it inside iterator type and hide from using directly.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---
 fs/proc/base.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 4eec684baca9..7c1089226a47 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3540,8 +3540,10 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
 struct tgid_iter {
 	unsigned int tgid;
 	struct task_struct *task;
+	struct pid_namespace *pid_ns;
 };
-static struct tgid_iter next_tgid(struct pid_namespace *ns, struct tgid_iter iter)
+
+static struct tgid_iter next_tgid(struct tgid_iter iter)
 {
 	struct pid *pid;
 
@@ -3550,9 +3552,9 @@ static struct tgid_iter next_tgid(struct pid_namespace *ns, struct tgid_iter ite
 	rcu_read_lock();
 retry:
 	iter.task = NULL;
-	pid = find_ge_pid(iter.tgid, ns);
+	pid = find_ge_pid(iter.tgid, iter.pid_ns);
 	if (pid) {
-		iter.tgid = pid_nr_ns(pid, ns);
+		iter.tgid = pid_nr_ns(pid, iter.pid_ns);
 		iter.task = pid_task(pid, PIDTYPE_TGID);
 		if (!iter.task) {
 			iter.tgid += 1;
@@ -3571,7 +3573,7 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
 {
 	struct tgid_iter iter;
 	struct proc_fs_info *fs_info = proc_sb_info(file_inode(file)->i_sb);
-	struct pid_namespace *ns = proc_pid_ns(file_inode(file)->i_sb);
+	struct pid_namespace *pid_ns = proc_pid_ns(file_inode(file)->i_sb);
 	loff_t pos = ctx->pos;
 
 	if (pos >= PID_MAX_LIMIT + TGID_OFFSET)
@@ -3589,9 +3591,10 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
 	}
 	iter.tgid = pos - TGID_OFFSET;
 	iter.task = NULL;
-	for (iter = next_tgid(ns, iter);
+	iter.pid_ns = pid_ns;
+	for (iter = next_tgid(iter);
 	     iter.task;
-	     iter.tgid += 1, iter = next_tgid(ns, iter)) {
+	     iter.tgid += 1, iter = next_tgid(iter)) {
 		char name[10 + 1];
 		unsigned int len;
 
-- 
2.51.2

[PATCH v2 2/2] proc: rewrite next_tgid()

[Alexey Dobriyan]

* deduplicate "iter.tgid += 1" line,
  it is done once inside next_tgid() itself and second time inside
  "for" loop

* deduplicate next_tgid() call itself with different loop style:

	auto it = make_xxx_iter();
	while (next_xxx(&it)) {
	}

  gcc seems to inline it twice in the original code:

  	$ ./scripts/bloat-o-meter ../vmlinux-000 ../obj/vmlinux
	add/remove: 0/1 grow/shrink: 1/0 up/down: 100/-245 (-145)
	Function                                     old     new   delta
	proc_pid_readdir                             531     631    +100
	next_tgid                                    245       -    -245

But if there is only one call, it doesn't matter if it is inlined or not!

* make tgid_iter.pid_ns const
  it never changes during readdir, returning instance + C99 initializer
  make it possible,

* rename "iter" to "it", this is what another language seems to be doing.

* limit declaration scope to prevent problems (in general).
---
 fs/proc/base.c | 69 ++++++++++++++++++++++++++++----------------------
 1 file changed, 39 insertions(+), 30 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 7c1089226a47..ddf5e16c795b 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3535,35 +3535,48 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
 
 /*
  * Find the first task with tgid >= tgid
- *
  */
 struct tgid_iter {
 	unsigned int tgid;
 	struct task_struct *task;
-	struct pid_namespace *pid_ns;
+	struct pid_namespace *const pid_ns;
 };
 
-static struct tgid_iter next_tgid(struct tgid_iter iter)
+static
+struct tgid_iter
+make_tgid_iter(unsigned int init_tgid, struct pid_namespace *pid_ns)
 {
-	struct pid *pid;
+	return (struct tgid_iter){
+		/* See preincrement below. */
+		.tgid = init_tgid - 1,
+		.pid_ns = pid_ns,
+	};
+}
+
+static bool next_tgid(struct tgid_iter *it)
+{
+	if (it->task) {
+		put_task_struct(it->task);
+		it->task = NULL;
+	}
 
-	if (iter.task)
-		put_task_struct(iter.task);
 	rcu_read_lock();
-retry:
-	iter.task = NULL;
-	pid = find_ge_pid(iter.tgid, iter.pid_ns);
-	if (pid) {
-		iter.tgid = pid_nr_ns(pid, iter.pid_ns);
-		iter.task = pid_task(pid, PIDTYPE_TGID);
-		if (!iter.task) {
-			iter.tgid += 1;
-			goto retry;
+	while (1) {
+		it->tgid += 1;
+		struct pid *pid = find_ge_pid(it->tgid, it->pid_ns);
+		if (pid) {
+			it->tgid = pid_nr_ns(pid, it->pid_ns);
+			it->task = pid_task(pid, PIDTYPE_TGID);
+			if (it->task) {
+				get_task_struct(it->task);
+				rcu_read_unlock();
+				return true;
+			}
+		} else {
+			rcu_read_unlock();
+			return false;
 		}
-		get_task_struct(iter.task);
 	}
-	rcu_read_unlock();
-	return iter;
 }
 
 #define TGID_OFFSET (FIRST_PROCESS_ENTRY + 2)
@@ -3571,7 +3584,6 @@ static struct tgid_iter next_tgid(struct tgid_iter iter)
 /* for the /proc/ directory itself, after non-process stuff has been done */
 int proc_pid_readdir(struct file *file, struct dir_context *ctx)
 {
-	struct tgid_iter iter;
 	struct proc_fs_info *fs_info = proc_sb_info(file_inode(file)->i_sb);
 	struct pid_namespace *pid_ns = proc_pid_ns(file_inode(file)->i_sb);
 	loff_t pos = ctx->pos;
@@ -3589,24 +3601,21 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
 			return 0;
 		ctx->pos = pos = pos + 1;
 	}
-	iter.tgid = pos - TGID_OFFSET;
-	iter.task = NULL;
-	iter.pid_ns = pid_ns;
-	for (iter = next_tgid(iter);
-	     iter.task;
-	     iter.tgid += 1, iter = next_tgid(iter)) {
+
+	auto it = make_tgid_iter(pos - TGID_OFFSET, pid_ns);
+	while (next_tgid(&it)) {
 		char name[10 + 1];
 		unsigned int len;
 
 		cond_resched();
-		if (!has_pid_permissions(fs_info, iter.task, HIDEPID_INVISIBLE))
+		if (!has_pid_permissions(fs_info, it.task, HIDEPID_INVISIBLE))
 			continue;
 
-		len = snprintf(name, sizeof(name), "%u", iter.tgid);
-		ctx->pos = iter.tgid + TGID_OFFSET;
+		len = snprintf(name, sizeof(name), "%u", it.tgid);
+		ctx->pos = it.tgid + TGID_OFFSET;
 		if (!proc_fill_cache(file, ctx, name, len,
-				     proc_pid_instantiate, iter.task, NULL)) {
-			put_task_struct(iter.task);
+				     proc_pid_instantiate, it.task, NULL)) {
+			put_task_struct(it.task);
 			return 0;
 		}
 	}
-- 
2.51.2