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| author | Peter Zijlstra <peterz@infradead.org> | 2011-06-22 11:20:09 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2011-06-22 11:39:34 +0200 |
| commit | 4f2a8d3cf5e0486fd547633fa86c5d130ae98cad (patch) | |
| tree | 4f60a635565fd63473e5c23f45745b3b502a1d52 /kernel/printk.c | |
| parent | 0b5e1c5255e7ee8670e077e8224e5c2281229a5b (diff) | |
| download | lwn-4f2a8d3cf5e0486fd547633fa86c5d130ae98cad.tar.gz lwn-4f2a8d3cf5e0486fd547633fa86c5d130ae98cad.zip | |
printk: Fix console_sem vs logbuf_lock unlock race
Fix up the fallout from commit 0b5e1c5255 ("printk: Release
console_sem after logbuf_lock").
The reason for unlocking the console_sem under the logbuf_lock
is that a concurrent printk() might fill up the buffer but fail
to acquire the console sem, resulting in a missed write to the
console until a subsequent console_sem acquire/release cycle.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: efault@gmx.de
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1308734409.1022.14.camel@twins
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/printk.c')
| -rw-r--r-- | kernel/printk.c | 20 |
1 files changed, 18 insertions, 2 deletions
diff --git a/kernel/printk.c b/kernel/printk.c index 751e7b84e9e3..37dff3429adb 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -1244,7 +1244,7 @@ void console_unlock(void) { unsigned long flags; unsigned _con_start, _log_end; - unsigned wake_klogd = 0; + unsigned wake_klogd = 0, retry = 0; if (console_suspended) { up(&console_sem); @@ -1253,6 +1253,7 @@ void console_unlock(void) console_may_schedule = 0; +again: for ( ; ; ) { spin_lock_irqsave(&logbuf_lock, flags); wake_klogd |= log_start - log_end; @@ -1273,8 +1274,23 @@ void console_unlock(void) if (unlikely(exclusive_console)) exclusive_console = NULL; - spin_unlock_irqrestore(&logbuf_lock, flags); + spin_unlock(&logbuf_lock); + up(&console_sem); + + /* + * Someone could have filled up the buffer again, so re-check if there's + * something to flush. In case we cannot trylock the console_sem again, + * there's a new owner and the console_unlock() from them will do the + * flush, no worries. + */ + spin_lock(&logbuf_lock); + if (con_start != log_end) + retry = 1; + spin_unlock_irqrestore(&logbuf_lock, flags); + if (retry && console_trylock()) + goto again; + if (wake_klogd) wake_up_klogd(); } |