On 08/08, Linus Torvalds wrote: > > As a result, doing a "recalc_sigpending_and_wake(()"
and btw it should die, I think. > is definitely > incorrect, because sigpending state cannot actually have changed. Yes, if we need to wakeup in this case something is already wrong. > - somebody setting TASK_SLEEPING -> __schedule() testing the > signal_pending_state() > > and as far as I can tell we have proper barriers for those (the > scheduler gets the rq lock Yes, but... ttwu() takse another lock, ->pi_lock to test ->state. This looks racy, even if wmb() actually acts as mb(), we don't have mb() on the other side and schedule() can miss SIGPENDING? Unless the task does set_current_state(TASK_INTERRUPTIBLE) which adds mb(). But, just for example, sigsuspend() relies on schedule(). > smp_wmb(); > raw_spin_lock_irqsave(&p->pi_lock, flags); > if (!(p->state & state)) > > before it tests the task state. And the wmb() *together* with the > spinlock really should be a full memory barrier (nothing can get out > from the spinlock, and any writes before this had better be serialized > by the wmb and the write inherent in the spinlock itself). But this is > definitely some subtle stuff. So perhaps it makes sense to re-test after s/smp_wmb/smp_mb/ ? And perhaps we can add smp_mb__before_lock(), we alredy have smp_mb__after_lock(). And of course, there could be another bug. I just did "grep recalc_sigpending" and immediately found at least one buggy user, fs/dlm/user.c which calls it lockless. > > Every time Xorg hangs up, the status of Xorg is read as following(cat > > /proc/2597/status): Gao, could you show /proc/pid/stack just in case? Oleg. -- 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/
