[PATCH] lockdep: do not recurse in printk

Make printk()-ing from within the lock validation code safer by using the
lockdep-recursion counter.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 18 insertions, 5 deletions

diff --git a/kernel/printk.c b/kernel/printk.c
index 39ae24d2a415..bdba5d80496c 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -518,7 +518,9 @@ asmlinkage int vprintk(const char *fmt, va_list args)
                 zap_locks();
 
         /* This stops the holder of console_sem just where we want him */
-        spin_lock_irqsave(&logbuf_lock, flags);
+        local_irq_save(flags);
+        lockdep_off();
+        spin_lock(&logbuf_lock);
         printk_cpu = smp_processor_id();
 
         /* Emit the output into the temporary buffer */
@@ -588,7 +590,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
                  */
                 console_locked = 1;
                 printk_cpu = UINT_MAX;
-                spin_unlock_irqrestore(&logbuf_lock, flags);
+                spin_unlock(&logbuf_lock);
 
                 /*
                  * Console drivers may assume that per-cpu resources have
@@ -604,6 +606,8 @@ asmlinkage int vprintk(const char *fmt, va_list args)
                         console_locked = 0;
                         up(&console_sem);
                 }
+                lockdep_on();
+                local_irq_restore(flags);
         } else {
                 /*
                  * Someone else owns the drivers.  We drop the spinlock, which
@@ -611,7 +615,9 @@ asmlinkage int vprintk(const char *fmt, va_list args)
                  * console drivers with the output which we just produced.
                  */
                 printk_cpu = UINT_MAX;
-                spin_unlock_irqrestore(&logbuf_lock, flags);
+                spin_unlock(&logbuf_lock);
+                lockdep_on();
+                local_irq_restore(flags);
         }
 
         preempt_enable();
@@ -809,8 +815,15 @@ void release_console_sem(void)
         console_may_schedule = 0;
         up(&console_sem);
         spin_unlock_irqrestore(&logbuf_lock, flags);
-        if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
-                wake_up_interruptible(&log_wait);
+        if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait)) {
+                /*
+                 * If we printk from within the lock dependency code,
+                 * from within the scheduler code, then do not lock
+                 * up due to self-recursion:
+                 */
+                if (!lockdep_internal())
+                        wake_up_interruptible(&log_wait);
+        }
 }
 EXPORT_SYMBOL(release_console_sem);