printk: avoid double lock acquire

Commit 4f2a8d3cf5e ("printk: Fix console_sem vs logbuf_lock unlock race")
introduced another silly bug where we would want to acquire an already
held lock.  Avoid this.

Reported-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/printk.c b/kernel/printk.c
index 1455a0d..7982a0a 100644 (file)
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1293,10 +1293,11 @@ again:
        raw_spin_lock(&logbuf_lock);
        if (con_start != log_end)
                retry = 1;
        raw_spin_lock(&logbuf_lock);
        if (con_start != log_end)
                retry = 1;

+       raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+

        if (retry && console_trylock())
                goto again;
 
        if (retry && console_trylock())
                goto again;
 

-       raw_spin_unlock_irqrestore(&logbuf_lock, flags);

        if (wake_klogd)
                wake_up_klogd();
 }
        if (wake_klogd)
                wake_up_klogd();
 }