Commit-ID: 9c368b5b6eccce1cbd7f68142106b3b4ddb1c5b5
Gitweb: http://git.kernel.org/tip/9c368b5b6eccce1cbd7f68142106b3b4ddb1c5b5
Author: Rik van Riel <riel@xxxxxxxxxx>
AuthorDate: Fri, 12 Sep 2014 09:12:15 -0400
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 19 Sep 2014 12:35:17 +0200
sched, time: Fix lock inversion in thread_group_cputime()
The sig->stats_lock nests inside the tasklist_lock and the
sighand->siglock in __exit_signal and wait_task_zombie.
However, both of those locks can be taken from irq context,
which means we need to use the interrupt safe variant of
read_seqbegin_or_lock. This blocks interrupts when the "lock"
branch is taken (seq is odd), preventing the lock inversion.
On the first (lockless) pass through the loop, irqs are not
blocked.
Reported-by: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: prarit@xxxxxxxxxx
Cc: oleg@xxxxxxxxxx
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1410527535-9814-3-git-send-email-riel@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/cputime.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 2b57031..64492df 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -289,13 +289,14 @@ void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
cputime_t utime, stime;
struct task_struct *t;
unsigned int seq, nextseq;
+ unsigned long flags;
rcu_read_lock();
/* Attempt a lockless read on the first round. */
nextseq = 0;
do {
seq = nextseq;
- read_seqbegin_or_lock(&sig->stats_lock, &seq);
+ flags = read_seqbegin_or_lock_irqsave(&sig->stats_lock, &seq);
times->utime = sig->utime;
times->stime = sig->stime;
times->sum_exec_runtime = sig->sum_sched_runtime;
@@ -309,7 +310,7 @@ void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
/* If lockless access failed, take the lock. */
nextseq = 1;
} while (need_seqretry(&sig->stats_lock, seq));
- done_seqretry(&sig->stats_lock, seq);
+ done_seqretry_irqrestore(&sig->stats_lock, seq, flags);
rcu_read_unlock();
}
--
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