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Subject[patch 32/61] lock validator: do not recurse in printk()
From: Ingo Molnar <mingo@elte.hu>

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>
---
kernel/printk.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

Index: linux/kernel/printk.c
===================================================================
--- linux.orig/kernel/printk.c
+++ linux/kernel/printk.c
@@ -516,7 +516,9 @@ asmlinkage int vprintk(const char *fmt,
zap_locks();

/* This stops the holder of console_sem just where we want him */
- spin_lock_irqsave(&logbuf_lock, flags);
+ local_irq_save(flags);
+ current->lockdep_recursion++;
+ spin_lock(&logbuf_lock);
printk_cpu = smp_processor_id();

/* Emit the output into the temporary buffer */
@@ -586,7 +588,7 @@ asmlinkage int vprintk(const char *fmt,
*/
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
@@ -602,6 +604,8 @@ asmlinkage int vprintk(const char *fmt,
console_locked = 0;
up(&console_sem);
}
+ current->lockdep_recursion--;
+ local_irq_restore(flags);
} else {
/*
* Someone else owns the drivers. We drop the spinlock, which
@@ -609,7 +613,9 @@ asmlinkage int vprintk(const char *fmt,
* console drivers with the output which we just produced.
*/
printk_cpu = UINT_MAX;
- spin_unlock_irqrestore(&logbuf_lock, flags);
+ spin_unlock(&logbuf_lock);
+ current->lockdep_recursion--;
+ local_irq_restore(flags);
}

preempt_enable();
@@ -783,7 +789,13 @@ void release_console_sem(void)
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 we printk from within the lock dependency code,
+ * from within the scheduler code, then do not lock
+ * up due to self-recursion:
+ */
+ if (current->lockdep_recursion <= 1)
+ wake_up_interruptible(&log_wait);
}
EXPORT_SYMBOL(release_console_sem);

-
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