Re: Errors and later panics in 2.6.0-test11.

[Linus Torvalds]

On Wed, 3 Dec 2003, David Martínez Moreno wrote:
>
> 	I've just rebooted about six hours ago, and it's giving panics elsewhere:
>
> [...]
> Ending XFS recovery on filesystem: md0 (dev: md0)
> b44: eth0: Link is down.
> b44: eth0: Link is up at 100 Mbps, full duplex.
> b44: eth0: Flow control is on for TX and on for RX.
> eth0: no IPv6 routers present
> Unable to handle kernel paging request at virtual address 00100104

That's the LIST_POISON stuff: 00100100 is the "bad list pointer". Somebody
tried to remove a page twice.

Doesn't mean a lot - if your "struct page" got corrupted, anything can
happen. Quite possibly it's a double free.

> 	I can rebuild the Debian mirror for not using the RAID and using the SATA
> disks separately, but will be tomorrow, it's a lot of space to move, and I
> need remote intervention.
>
> 	Anyway I'd love to know before doing if it will be useful, looking at what
> Jens has said just ten minutes ago about RAIDs 0/5. Will it help to you? Say
> so and I'll go for it.

It might be more useful to leave it as RAID0, if you're willing to try out
patches to try to debug this. The slab-debugging thing I sent out earlier
is one such patch (but may well cause out-of-memory problems under load),
and possibly the atomic-decrement checker patch (appended). And maybe Jens
and Neil can come up with something..

		Linus

----
===== arch/i386/lib/dec_and_lock.c 1.1 vs edited =====
--- 1.1/arch/i386/lib/dec_and_lock.c	Tue Feb  5 09:40:21 2002
+++ edited/arch/i386/lib/dec_and_lock.c	Sun Nov  2 09:07:53 2003
@@ -19,7 +19,7 @@
 	counter = atomic_read(atomic);
 	newcount = counter-1;

-	if (!newcount)
+	if (newcount <= 0)
 		goto slow_path;

 	asm volatile("lock; cmpxchgl %1,%2"
===== include/asm-i386/atomic.h 1.5 vs edited =====
--- 1.5/include/asm-i386/atomic.h	Mon Aug 18 19:46:23 2003
+++ edited/include/asm-i386/atomic.h	Sun Nov  2 09:40:42 2003
@@ -2,6 +2,8 @@
 #define __ARCH_I386_ATOMIC__

 #include <linux/config.h>
+#include <linux/kernel.h>
+#include <asm/bug.h>

 /*
  * Atomic operations that C can't guarantee us.  Useful for
@@ -136,12 +138,17 @@
  */
 static __inline__ int atomic_dec_and_test(atomic_t *v)
 {
-	unsigned char c;
+	static int count = 2;
+	unsigned char c, neg;

 	__asm__ __volatile__(
-		LOCK "decl %0; sete %1"
-		:"=m" (v->counter), "=qm" (c)
+		LOCK "decl %0; sete %1; sets %2"
+		:"=m" (v->counter), "=qm" (c), "=qm" (neg)
 		:"m" (v->counter) : "memory");
+	if (count && neg) {
+		count--;
+		WARN_ON(neg);
+	}
 	return c != 0;
 }

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