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| author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2011-06-07 11:15:33 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2011-06-07 12:50:02 +0200 |
| commit | 0b5e1c5255e7ee8670e077e8224e5c2281229a5b (patch) | |
| tree | eb6f967b14d69553e380ab2f13a2dcd8789e865e /kernel/printk.c | |
| parent | 59c5f46fbe01a00eedf54a23789634438bb80603 (diff) | |
| download | lwn-0b5e1c5255e7ee8670e077e8224e5c2281229a5b.tar.gz lwn-0b5e1c5255e7ee8670e077e8224e5c2281229a5b.zip | |
printk: Release console_sem after logbuf_lock
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>
Diffstat (limited to 'kernel/printk.c')
| -rw-r--r-- | kernel/printk.c | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/kernel/printk.c b/kernel/printk.c index 35185392173f..751e7b84e9e3 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -782,7 +782,7 @@ static inline int can_use_console(unsigned int cpu) static int console_trylock_for_printk(unsigned int cpu) __releases(&logbuf_lock) { - int retval = 0; + int retval = 0, wake = 0; if (console_trylock()) { retval = 1; @@ -795,12 +795,14 @@ static int console_trylock_for_printk(unsigned int cpu) */ if (!can_use_console(cpu)) { console_locked = 0; - up(&console_sem); + wake = 1; retval = 0; } } printk_cpu = UINT_MAX; spin_unlock(&logbuf_lock); + if (wake) + up(&console_sem); return retval; } static const char recursion_bug_msg [] = @@ -1271,8 +1273,8 @@ void console_unlock(void) if (unlikely(exclusive_console)) exclusive_console = NULL; - up(&console_sem); spin_unlock_irqrestore(&logbuf_lock, flags); + up(&console_sem); if (wake_klogd) wake_up_klogd(); } |