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printk: Release console_sem after logbuf_lock

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Release console_sem after unlocking the logbuf_lock so that we don't
generate wakeups while holding logbuf_lock. This avoids some lock
inversion troubles once we remove the lockdep_off bits between
logbuf_lock and rq->lock (prints while holding rq->lock vs doing
wakeups while holding logbuf_lock).

There's of course still an actual deadlock where the printk()s under
rq->lock will issue a wakeup from the up() call, but lockdep won't
warn about that since semaphores are not tracked.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-j8swthl12u73h4znbvitljzd@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2011-06-07 11:15:33 +02:00 committed by Ingo Molnar
parent 59c5f46fbe
commit 0b5e1c5255
1 changed files with 5 additions and 3 deletions
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8
kernel/printk.c
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@ -782,7 +782,7 @@ static inline int can_use_console(unsigned int cpu)
static int console_trylock_for_printk(unsigned int cpu) static int console_trylock_for_printk(unsigned int cpu)
__releases(&logbuf_lock) __releases(&logbuf_lock)
{ {
int retval = 0; int retval = 0, wake = 0;
if (console_trylock()) { if (console_trylock()) {
retval = 1; retval = 1;
@ -795,12 +795,14 @@ static int console_trylock_for_printk(unsigned int cpu)
*/ */
if (!can_use_console(cpu)) { if (!can_use_console(cpu)) {
console_locked = 0; console_locked = 0;
up(&console_sem); wake = 1;
retval = 0; retval = 0;
} }
} }
printk_cpu = UINT_MAX; printk_cpu = UINT_MAX;
spin_unlock(&logbuf_lock); spin_unlock(&logbuf_lock);
if (wake)
up(&console_sem);
return retval; return retval;
} }
static const char recursion_bug_msg [] = static const char recursion_bug_msg [] =
@ -1271,8 +1273,8 @@ void console_unlock(void)
if (unlikely(exclusive_console)) if (unlikely(exclusive_console))
exclusive_console = NULL; exclusive_console = NULL;
up(&console_sem);
spin_unlock_irqrestore(&logbuf_lock, flags); spin_unlock_irqrestore(&logbuf_lock, flags);
up(&console_sem);
if (wake_klogd) if (wake_klogd)
wake_up_klogd(); wake_up_klogd();
} }