[patch] slab.c ATOMIC debug check to immediately trap atomic abuse

[Henrik Nordstrom]

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Hi.

The attached patch extends slab debugging with an early check if ATOMIC
is required. The patch is relative to 2.4.20 but may also be interesting
for 2.5.

Normally the atomic requirement is only verified when the slab cache
needs to grow, but with this patch such errors is detected immediately
on first call if slab debugging is enabled.

This patch would have saved me from panic bug hunting after a system was
sent into production as the errors then would have been trapped
immediately during development. Probably many others would be helped by
this slab debugging to trap stupid memory allocation / locking errors
early on in development.

Regards
Henrik Nordstrvm
MARA Systems AB, Sweden

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--- linux-2.4.20-uml/mm/slab.c	2003-02-27 20:56:12.000000000 +0100
+++ linux-2.4.20-uml-henrik/mm/slab.c	2003-05-26 20:57:44.000000000 +0200
@@ -1338,6 +1338,12 @@
 	unsigned long save_flags;
 	void* objp;
 
+#if DEBUG
+	/* trap atomic bugs early on when debugging */
+	if (in_interrupt() && (flags & SLAB_LEVEL_MASK) != SLAB_ATOMIC)
+		BUG();
+#endif
+
 	kmem_cache_alloc_head(cachep, flags);
 try_again:
 	local_irq_save(save_flags);

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