Commit 4f2a8d3c authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar

printk: Fix console_sem vs logbuf_lock unlock race

Fix up the fallout from commit 0b5e1c52 ("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: default avatarPeter 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@twinsSigned-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 0b5e1c52
...@@ -1244,7 +1244,7 @@ void console_unlock(void) ...@@ -1244,7 +1244,7 @@ void console_unlock(void)
{ {
unsigned long flags; unsigned long flags;
unsigned _con_start, _log_end; unsigned _con_start, _log_end;
unsigned wake_klogd = 0; unsigned wake_klogd = 0, retry = 0;
if (console_suspended) { if (console_suspended) {
up(&console_sem); up(&console_sem);
...@@ -1253,6 +1253,7 @@ void console_unlock(void) ...@@ -1253,6 +1253,7 @@ void console_unlock(void)
console_may_schedule = 0; console_may_schedule = 0;
again:
for ( ; ; ) { for ( ; ; ) {
spin_lock_irqsave(&logbuf_lock, flags); spin_lock_irqsave(&logbuf_lock, flags);
wake_klogd |= log_start - log_end; wake_klogd |= log_start - log_end;
...@@ -1273,8 +1274,23 @@ void console_unlock(void) ...@@ -1273,8 +1274,23 @@ void console_unlock(void)
if (unlikely(exclusive_console)) if (unlikely(exclusive_console))
exclusive_console = NULL; exclusive_console = NULL;
spin_unlock_irqrestore(&logbuf_lock, flags); spin_unlock(&logbuf_lock);
up(&console_sem); 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) if (wake_klogd)
wake_up_klogd(); wake_up_klogd();
} }
......
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