* [PATCH rcu 2/3] refscale: Fix uninitalized use of wait_queue_head_t
2023-07-17 18:07 [PATCH rcu 0/3] Reference-side scalability test updates for v6.6 Paul E. McKenney
2023-07-17 18:10 ` [PATCH rcu 1/3] refscale: Add CONFIG_PREEMPT_DYNAMIC=n to NOPREEMPT scenario Paul E. McKenney
@ 2023-07-17 18:10 ` Paul E. McKenney
2023-07-17 18:10 ` [PATCH rcu 3/3] refscale: Add a "jiffies" test Paul E. McKenney
2 siblings, 0 replies; 4+ messages in thread
From: Paul E. McKenney @ 2023-07-17 18:10 UTC (permalink / raw)
To: rcu
Cc: linux-kernel, kernel-team, rostedt, Waiman Long, Qiuxu Zhuo,
Davidlohr Bueso, Joel Fernandes, Paul E . McKenney
From: Waiman Long <longman@redhat.com>
Running the refscale test occasionally crashes the kernel with the
following error:
[ 8569.952896] BUG: unable to handle page fault for address: ffffffffffffffe8
[ 8569.952900] #PF: supervisor read access in kernel mode
[ 8569.952902] #PF: error_code(0x0000) - not-present page
[ 8569.952904] PGD c4b048067 P4D c4b049067 PUD c4b04b067 PMD 0
[ 8569.952910] Oops: 0000 [#1] PREEMPT_RT SMP NOPTI
[ 8569.952916] Hardware name: Dell Inc. PowerEdge R750/0WMWCR, BIOS 1.2.4 05/28/2021
[ 8569.952917] RIP: 0010:prepare_to_wait_event+0x101/0x190
:
[ 8569.952940] Call Trace:
[ 8569.952941] <TASK>
[ 8569.952944] ref_scale_reader+0x380/0x4a0 [refscale]
[ 8569.952959] kthread+0x10e/0x130
[ 8569.952966] ret_from_fork+0x1f/0x30
[ 8569.952973] </TASK>
The likely cause is that init_waitqueue_head() is called after the call to
the torture_create_kthread() function that creates the ref_scale_reader
kthread. Although this init_waitqueue_head() call will very likely
complete before this kthread is created and starts running, it is
possible that the calling kthread will be delayed between the calls to
torture_create_kthread() and init_waitqueue_head(). In this case, the
new kthread will use the waitqueue head before it is properly initialized,
which is not good for the kernel's health and well-being.
The above crash happened here:
static inline void __add_wait_queue(...)
{
:
if (!(wq->flags & WQ_FLAG_PRIORITY)) <=== Crash here
The offset of flags from list_head entry in wait_queue_entry is
-0x18. If reader_tasks[i].wq.head.next is NULL as allocated reader_task
structure is zero initialized, the instruction will try to access address
0xffffffffffffffe8, which is exactly the fault address listed above.
This commit therefore invokes init_waitqueue_head() before creating
the kthread.
Fixes: 653ed64b01dc ("refperf: Add a test to measure performance of read-side synchronization")
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/refscale.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index 1970ce5f22d4..71d138573856 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -1107,12 +1107,11 @@ ref_scale_init(void)
VERBOSE_SCALEOUT("Starting %d reader threads", nreaders);
for (i = 0; i < nreaders; i++) {
+ init_waitqueue_head(&reader_tasks[i].wq);
firsterr = torture_create_kthread(ref_scale_reader, (void *)i,
reader_tasks[i].task);
if (torture_init_error(firsterr))
goto unwind;
-
- init_waitqueue_head(&(reader_tasks[i].wq));
}
// Main Task
--
2.40.1
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH rcu 3/3] refscale: Add a "jiffies" test
2023-07-17 18:07 [PATCH rcu 0/3] Reference-side scalability test updates for v6.6 Paul E. McKenney
2023-07-17 18:10 ` [PATCH rcu 1/3] refscale: Add CONFIG_PREEMPT_DYNAMIC=n to NOPREEMPT scenario Paul E. McKenney
2023-07-17 18:10 ` [PATCH rcu 2/3] refscale: Fix uninitalized use of wait_queue_head_t Paul E. McKenney
@ 2023-07-17 18:10 ` Paul E. McKenney
2 siblings, 0 replies; 4+ messages in thread
From: Paul E. McKenney @ 2023-07-17 18:10 UTC (permalink / raw)
To: rcu; +Cc: linux-kernel, kernel-team, rostedt, Paul E. McKenney
This commit adds a "jiffies" test to refscale, allowing use of jiffies
to be compared to ktime_get_real_fast_ns(). On my x86 laptop, jiffies
is more than 20x faster. (Though for many uses, the tens-of-nanoseconds
overhead of ktime_get_real_fast_ns() will be just fine.)
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/refscale.c | 34 +++++++++++++++++++++++++++++++++-
1 file changed, 33 insertions(+), 1 deletion(-)
diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index 71d138573856..91a0fd0d4d9a 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -528,6 +528,38 @@ static struct ref_scale_ops clock_ops = {
.name = "clock"
};
+static void ref_jiffies_section(const int nloops)
+{
+ u64 x = 0;
+ int i;
+
+ preempt_disable();
+ for (i = nloops; i >= 0; i--)
+ x += jiffies;
+ preempt_enable();
+ stopopts = x;
+}
+
+static void ref_jiffies_delay_section(const int nloops, const int udl, const int ndl)
+{
+ u64 x = 0;
+ int i;
+
+ preempt_disable();
+ for (i = nloops; i >= 0; i--) {
+ x += jiffies;
+ un_delay(udl, ndl);
+ }
+ preempt_enable();
+ stopopts = x;
+}
+
+static struct ref_scale_ops jiffies_ops = {
+ .readsection = ref_jiffies_section,
+ .delaysection = ref_jiffies_delay_section,
+ .name = "jiffies"
+};
+
////////////////////////////////////////////////////////////////////////
//
// Methods leveraging SLAB_TYPESAFE_BY_RCU.
@@ -1047,7 +1079,7 @@ ref_scale_init(void)
int firsterr = 0;
static struct ref_scale_ops *scale_ops[] = {
&rcu_ops, &srcu_ops, RCU_TRACE_OPS RCU_TASKS_OPS &refcnt_ops, &rwlock_ops,
- &rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops, &clock_ops,
+ &rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops, &clock_ops, &jiffies_ops,
&typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops,
};
--
2.40.1
^ permalink raw reply [flat|nested] 4+ messages in thread