* Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Sun, 2011-06-05 at 22:15 +0200, Arne Jansen wrote: > > > > Can lockdep just get confused by the lockdep_off/on calls in printk > > while scheduling is allowed? There aren't many users of lockdep_off(). > > Yes!, in that case lock_is_held() returns false, triggering the warning. > I guess there's an argument to be made in favour of the below.. > > --- > kernel/lockdep.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/kernel/lockdep.c b/kernel/lockdep.c > index 53a6895..e4129cf 100644 > --- a/kernel/lockdep.c > +++ b/kernel/lockdep.c > @@ -3242,7 +3242,7 @@ int lock_is_held(struct lockdep_map *lock) > int ret = 0; > > if (unlikely(current->lockdep_recursion)) > - return ret; > + return 1; /* avoid false negative lockdep_assert_held */ > > raw_local_irq_save(flags); > check_flags(flags); Oh, this explains the full bug i think. lockdep_off() causes us to not track pi_lock, and thus the assert inside printk() called try_to_wake_up() triggers incorrectly. The reason why Arne triggered it is probably because console_lock *wakeups* from printk are very, very rare: almost nothing actually locks the console. His remote system probably has some VT-intense application (screen?) that hits console_lock more intensely. Arne, do you use some vt-intense application there? The real fix might be to remove the lockdep_off()/on() call from printk(), that looks actively evil ... we had to hack through several layers of side-effects before we found the real bug - so it's not like the off()/on() made things more robust! So i think what we want to apply is the lockdep_off()/on() removal, once Arne has it tested. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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