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authorDavid Howells <dhowells@redhat.com>2005-09-06 15:16:34 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2005-09-07 16:57:18 -0700
commitfe21773d655c2c64641ec2cef499289ea175c817 (patch)
treeebc1f49f0b7135aa05bbf3a5463a6e1c238add89
parentc3d8c1414573be8cf7c8fdc1e076935697c7f6af (diff)
[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 <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--kernel/printk.c13
1 files changed, 12 insertions, 1 deletions
diff --git a/kernel/printk.c b/kernel/printk.c
index 5092397fac2..a967605bc2e 100644
--- 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, va_list args)
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, va_list args)
* 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, va_list args)
* 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, va_list args)
* 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);