From: Rik van Riel <[email protected]> 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. Signed-off-by: Rik van Riel <[email protected]> Reported-by: Stanislaw Gruszka <[email protected]> --- 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(); } -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
