tree ebc1f49f0b7135aa05bbf3a5463a6e1c238add89
parent c3d8c1414573be8cf7c8fdc1e076935697c7f6af
author David Howells <[EMAIL PROTECTED]> Wed, 07 Sep 2005 05:16:34 -0700
committer Linus Torvalds <[EMAIL PROTECTED]> Thu, 08 Sep 2005 06:57:18 -0700
[PATCH] Provide better printk() support for SMP machines
The attached patch prevents oopses interleaving with characters from
other printks on other CPUs by only breaking the lock if the oops is
happening on the machine holding the lock.
It might be better if the oops generator got the lock and then called an
inner vprintk routine that assumed the caller holds the lock, thus
making oops reports "atomic".
Signed-Off-By: David Howells <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
kernel/printk.c | 13 ++++++++++++-
1 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/kernel/printk.c b/kernel/printk.c
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -514,6 +514,9 @@ asmlinkage int printk(const char *fmt, .
return r;
}
+/* cpu currently holding logbuf_lock */
+static volatile unsigned int printk_cpu = UINT_MAX;
+
asmlinkage int vprintk(const char *fmt, va_list args)
{
unsigned long flags;
@@ -522,11 +525,15 @@ asmlinkage int vprintk(const char *fmt,
static char printk_buf[1024];
static int log_level_unknown = 1;
- if (unlikely(oops_in_progress))
+ preempt_disable();
+ if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
+ /* If a crash is occurring during printk() on this CPU,
+ * make sure we can't deadlock */
zap_locks();
/* This stops the holder of console_sem just where we want him */
spin_lock_irqsave(&logbuf_lock, flags);
+ printk_cpu = smp_processor_id();
/* Emit the output into the temporary buffer */
printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
@@ -595,6 +602,7 @@ asmlinkage int vprintk(const char *fmt,
* CPU until it is officially up. We shouldn't be calling into
* random console drivers on a CPU which doesn't exist yet..
*/
+ printk_cpu = UINT_MAX;
spin_unlock_irqrestore(&logbuf_lock, flags);
goto out;
}
@@ -604,6 +612,7 @@ asmlinkage int vprintk(const char *fmt,
* We own the drivers. We can drop the spinlock and let
* release_console_sem() print the text
*/
+ printk_cpu = UINT_MAX;
spin_unlock_irqrestore(&logbuf_lock, flags);
console_may_schedule = 0;
release_console_sem();
@@ -613,9 +622,11 @@ asmlinkage int vprintk(const char *fmt,
* allows the semaphore holder to proceed and to call the
* console drivers with the output which we just produced.
*/
+ printk_cpu = UINT_MAX;
spin_unlock_irqrestore(&logbuf_lock, flags);
}
out:
+ preempt_enable();
return printed_len;
}
EXPORT_SYMBOL(printk);
-
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