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Commit 0b5e1c52 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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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: default avatarPeter 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: default avatarIngo Molnar <mingo@elte.hu>
parent 59c5f46f

kernel/printk.c

+5 −3
Original line number Diff line number Diff line
@@ -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();

}