Messages in this thread Patch in this message |  | | | Date | Mon, 9 Oct 2006 10:26:34 +0200 | | From | Ingo Molnar <> | | Subject | [patch] lockdep: fix printk recursion logic |
* Tilman Schmidt <tilman@imap.cc> wrote:
> Problem description: > > While X is running, output from printk() appears in syslog (eg. > > /var/log/messages) only after a key is pressed on the system keyboard, > > even though it is visible with dmesg immediately. > (from lkml message <450BF1CC.2070309@imap.cc> - see that message > for further details) > > The problem did not exist in 2.6.17, so I think it qualifies as a > regression. > > The following naive patch fixes the problem for me, without any > apparent ill effects (ie. the menace of lockup never manifested > itself): > > --- a/kernel/printk.c 2006-10-07 00:51:09.000000000 +0200 > +++ b/kernel/printk.c 2006-10-07 00:51:41.000000000 +0200 > @@ -826,8 +826,7 @@ void release_console_sem(void) > * from within the scheduler code, then do not lock > * up due to self-recursion: > */ > - if (!lockdep_internal()) > - wake_up_interruptible(&log_wait); > + wake_up_interruptible(&log_wait);
the reason is that i initially only had the chunk above to protect against lockdep recursion within vprintk() - it grew the 'outer' lockdep_off()/on() protection only later on. But that lockdep_off() made the release_console_sem() within vprintk() always happen under the lockdep_internal() condition, causing your bug.
so the right solution is your patch: to remove the inner protection against recursion here - the outer one is enough.
Andrew, could we use the patch below - it also removes a now stale comment. Also for -stable review i think.
Ingo
----------------> Subject: lockdep: fix printk recursion logic From: Ingo Molnar <mingo@elte.hu> bug reported and fixed by Tilman Schmidt <tilman@imap.cc>: if lockdep is enabled then log messages make it to /var/log/messages belatedly. The reason is a missed wakeup of klogd.
initially there was only a lockdep_internal() protection against lockdep recursion within vprintk() - it grew the 'outer' lockdep_off()/on() protection only later on. But that lockdep_off() made the release_console_sem() within vprintk() always happen under the lockdep_internal() condition, causing the bug.
the right solution to remove the inner protection against recursion here - the outer one is enough.
Signed-off-by: Ingo Molnar <mingo@elte.hu> --- kernel/printk.c | 11 ++--------- 1 file changed, 2 insertions(+), 9 deletions(-) Index: linux/kernel/printk.c =================================================================== --- linux.orig/kernel/printk.c +++ linux/kernel/printk.c @@ -801,15 +801,8 @@ void release_console_sem(void) console_locked = 0; up(&console_sem); spin_unlock_irqrestore(&logbuf_lock, flags); - if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait)) { - /* - * If we printk from within the lock dependency code, - * from within the scheduler code, then do not lock - * up due to self-recursion: - */ - if (!lockdep_internal()) - wake_up_interruptible(&log_wait); - } + if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait)) + wake_up_interruptible(&log_wait); } EXPORT_SYMBOL(release_console_sem); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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