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SubjectRe: sig->cputimer.lock/rq->lock lockdep report
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On Wed, 2011-10-12 at 23:13 +0300, Ari Savolainen wrote:
> I've got the same problem that Dave reported earlier. I bisected it to
> commit d670ec13178d "posix-cpu-timers: Cure SMP wobbles".

https://lkml.org/lkml/2011/10/7/282

Does the below work for you? (still not proud of it)

---
include/linux/sched.h | 3 +++
kernel/posix-cpu-timers.c | 6 +++++-
kernel/sched_stats.h | 4 ++--
3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 41d0237..ad9eafc 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -503,6 +503,7 @@ struct task_cputime {
* @running: non-zero when there are timers running and
* @cputime receives updates.
* @lock: lock for fields in this struct.
+ * @runtime_lock: lock for cputime.sum_exec_runtime
*
* This structure contains the version of task_cputime, above, that is
* used for thread group CPU timer calculations.
@@ -511,6 +512,7 @@ struct thread_group_cputimer {
struct task_cputime cputime;
int running;
spinlock_t lock;
+ spinlock_t runtime_lock;
};

#include <linux/rwsem.h>
@@ -2566,6 +2568,7 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times);
static inline void thread_group_cputime_init(struct signal_struct *sig)
{
spin_lock_init(&sig->cputimer.lock);
+ spin_lock_init(&sig->cputimer.runtime_lock);
}

/*
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index c8008dd..fa189a6 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -284,9 +284,13 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
* it.
*/
thread_group_cputime(tsk, &sum);
+ spin_lock(&cputimer->runtime_lock);
update_gt_cputime(&cputimer->cputime, &sum);
- }
+ } else
+ spin_lock(&cputimer->runtime_lock);
+
*times = cputimer->cputime;
+ spin_unlock(&cputimer->runtime_lock);
spin_unlock_irqrestore(&cputimer->lock, flags);
}

diff --git a/kernel/sched_stats.h b/kernel/sched_stats.h
index 331e01b..a7e2c1a 100644
--- a/kernel/sched_stats.h
+++ b/kernel/sched_stats.h
@@ -330,7 +330,7 @@ static inline void account_group_exec_runtime(struct task_struct *tsk,
if (!cputimer->running)
return;

- spin_lock(&cputimer->lock);
+ spin_lock(&cputimer->runtime_lock);
cputimer->cputime.sum_exec_runtime += ns;
- spin_unlock(&cputimer->lock);
+ spin_unlock(&cputimer->runtime_lock);
}


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