sched: fix warning in sched_setaffinity
PATCH 1/1 sched: fix warning in sched_setaffinity
Commit 8f9ea86fdf99b added some logic to sched_setaffinity that included a WARN when a per-task affinity assignment races with a cpuset update.
Specifically, we can have a race where a cpuset update results in the task affinity no longer being a subset of the cpuset. That's fine; we have a fallback to instead use the cpuset mask. However, we have a WARN set up that will trigger if the cpuset mask has no overlap at all with the requested task affinity. This shouldn't be a warning condition; its trivial to create this condition.
Reproduced the warning by the following setup:
- $PID inside a cpuset cgroup
- another thread repeatedly switching the cpuset cpus from 1-2 to just 1
- another thread repeatedly setting the $PID affinity (via taskset) to 2
--- kernel/sched/syscalls.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
kernel/sched/syscalls.c +1 -1
@@ -1321,7 +1321,7 @@ int __sched_setaffinity(struct task_struct *p, struct affinity_context *ctx)bool empty = !cpumask_and (new_mask, new_mask, ctx->user_mask); -if (WARN_ON_ONCE (empty)) +if (empty)cpumask_copy (new_mask, cpus_allowed); }__set_cpus_allowed_ptr (p, ctx);
Signature · 1 line
2.46.0.469.g59c65b2a67-goog
Quoted 40 lines · Josh Don
Commit
8f9ea86fdf99badded some logic tosched_setaffinitythat included a WARN when a per-task affinity assignment races with a cpuset update.Specifically, we can have a race where a cpuset update results in the task affinity no longer being a subset of the cpuset. That's fine; we have a fallback to instead use the cpuset mask. However, we have a WARN set up that will trigger if the cpuset mask has no overlap at all with the requested task affinity. This shouldn't be a warning condition; its trivial to create this condition.
Reproduced the warning by the following setup:
- $PID inside a cpuset cgroup
- another thread repeatedly switching the cpuset cpus from 1-2 to just 1
- another thread repeatedly setting the $PID affinity (via taskset) to 2Fixes 8f9ea86fdf99b ("sched: Always preserve the user requested cpumask")Signed-off-by Josh Don <[email protected]>Acked-by Waiman Long <[email protected]>Tested-by Madadi Vineeth Reddy <[email protected]>Acked-and-tested-by Vincent Guittot <[email protected]>--- kernel/sched/syscalls.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)kernel/sched/syscalls.c +1
-2@@ -1321,7 +1321,7 @@ int __sched_setaffinity(struct task_struct *p, struct affinity_context *ctx)bool empty = !cpumask_and (new_mask, new_mask, ctx->user_mask); -if (WARN_ON_ONCE (empty)) +if (empty)cpumask_copy (new_mask, cpus_allowed); }__set_cpus_allowed_ptr (p, ctx); --
Quoted 2 lines
2.46.0.469.g59c65b2a67-goog
Hey,
I wanted to bump this one last time. It's a pretty simple change that already has ACK's from 3 other folks, but has seemed to fall through the cracks [1].
Best,
Josh
[1] Timeline:
Original patch sent Aug 29 and quickly got ACK'd:
https://lkml.org/lkml/2024/8/29/1819
Pinged on Sep 30: https://lkml.org/lkml/2024/9/30/1528
Pinged on Oct 25: https://lkml.org/lkml/2024/10/25/1708
Resent as a new message on Nov 11: https://lkml.org/lkml/2024/11/11/1125
Peter Zijlstra
maintainerQuoted 46 lines · Josh Don
Quoted 40 lines · Josh Don
Commit
8f9ea86fdf99badded some logic tosched_setaffinitythat included a WARN when a per-task affinity assignment races with a cpuset update.Specifically, we can have a race where a cpuset update results in the task affinity no longer being a subset of the cpuset. That's fine; we have a fallback to instead use the cpuset mask. However, we have a WARN set up that will trigger if the cpuset mask has no overlap at all with the requested task affinity. This shouldn't be a warning condition; its trivial to create this condition.
Reproduced the warning by the following setup:
- $PID inside a cpuset cgroup
- another thread repeatedly switching the cpuset cpus from 1-2 to just 1
- another thread repeatedly setting the $PID affinity (via taskset) to 2Fixes 8f9ea86fdf99b ("sched: Always preserve the user requested cpumask")Signed-off-by Josh Don <[email protected]>Acked-by Waiman Long <[email protected]>Tested-by Madadi Vineeth Reddy <[email protected]>Acked-and-tested-by Vincent Guittot <[email protected]>--- kernel/sched/syscalls.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)kernel/sched/syscalls.c +1
-2@@ -1321,7 +1321,7 @@ int __sched_setaffinity(struct task_struct *p, struct affinity_context *ctx)bool empty = !cpumask_and (new_mask, new_mask, ctx->user_mask); -if (WARN_ON_ONCE (empty)) +if (empty)cpumask_copy (new_mask, cpus_allowed); }__set_cpus_allowed_ptr (p, ctx); --Quoted 2 lines
2.46.0.469.g59c65b2a67-goog
Hey,
Quoted 3 lines
I wanted to bump this one last time. It's a pretty simple change that already has ACK's from 3 other folks, but has seemed to fall through the cracks [1].
Got it, I'll stick it in tip/sched/urgent post -rc1 or so.
The following commit has been merged into the sched/core branch of tip:
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 70ee7947a29029736a1a06c73a48ff37674a851b Gitweb: https://git.kernel.org/tip/70ee7947a29029736a1a06c73a48ff37674a851b Author: Josh Don <[email protected]> AuthorDate: Mon, 11 Nov 2024 10:27:38 -08:00 Committer: Peter Zijlstra <[email protected]> CommitterDate: Mon, 02 Dec 2024 12:01:27 +01:00
sched: fix warning in sched_setaffinity
Commit 8f9ea86fdf99b added some logic to sched_setaffinity that included a WARN when a per-task affinity assignment races with a cpuset update.
Specifically, we can have a race where a cpuset update results in the task affinity no longer being a subset of the cpuset. That's fine; we have a fallback to instead use the cpuset mask. However, we have a WARN set up that will trigger if the cpuset mask has no overlap at all with the requested task affinity. This shouldn't be a warning condition; its trivial to create this condition.
Reproduced the warning by the following setup:
- $PID inside a cpuset cgroup
- another thread repeatedly switching the cpuset cpus from 1-2 to just 1
- another thread repeatedly setting the $PID affinity (via taskset) to 2
--- kernel/sched/syscalls.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
kernel/sched/syscalls.c +1 -1
@@ -1200,7 +1200,7 @@ int __sched_setaffinity(struct task_struct *p, struct affinity_context *ctx)bool empty = !cpumask_and (new_mask, new_mask, ctx->user_mask); -if (WARN_ON_ONCE (empty)) +if (empty)cpumask_copy (new_mask, cpus_allowed); }__set_cpus_allowed_ptr (p, ctx);