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>
diff --git a/kernel/printk.c b/kernel/printk.c
index 3518539..751e7b8 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -782,7 +782,7 @@
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 @@
*/
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 @@
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();
}