Re: AGP bogosities

[OGAWA Hirofumi]

Linus Torvalds <torvalds@xxxxxxxx> writes:

> Hmm.. We seem to not have any tests for the counts becoming negative, and
> this would seem to be an easy mistake to make considering that both I and 
> Dave did it.

I stole this from -mm.
-- 
OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>


From: Ingo Molnar <mingo@xxxxxxx>

The patch below will detect atomic counter underflows.  This has been
test-driven in the -RT patchset for some time.  qdisc_destroy() triggered
it sometimes (in a seemingly nonfatal way, during device shutdown) - with
DaveM suggesting that it is most likely a bug in the networking code.  So
it would be nice to have this in -mm for some time to validate all atomic
counters on a broader base.

Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---

 25-akpm/include/asm-i386/atomic.h |    4 ++++
 1 files changed, 4 insertions(+)

diff -puN include/asm-i386/atomic.h~detect-atomic-counter-underflows include/asm-i386/atomic.h
--- 25/include/asm-i386/atomic.h~detect-atomic-counter-underflows	Wed Nov  3 15:27:37 2004
+++ 25-akpm/include/asm-i386/atomic.h	Wed Nov  3 15:27:37 2004
@@ -132,6 +132,10 @@ static __inline__ int atomic_dec_and_tes
 {
 	unsigned char c;
 
+	if (!atomic_read(v)) {
+		printk("BUG: atomic counter underflow at:\n");
+		dump_stack();
+	}
 	__asm__ __volatile__(
 		LOCK "decl %0; sete %1"
 		:"=m" (v->counter), "=qm" (c)
_
-
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