From mboxrd@z Thu Jan 1 00:00:00 1970 From: omar.ramirez@ti.com (Omar Ramirez Luna) Date: Thu, 31 Mar 2011 14:15:23 -0600 Subject: [PATCH] ARM: BUG() dies silently Message-ID: <1301602523-9906-1-git-send-email-omar.ramirez@ti.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org There are some cases where the code generated for BUG() results into an infinite while loop without causing a null dereference, this ends on a kernel being stuck on a loop and the user without a clue of what happened. E.g.: lib/scatterlist.c : __sg_alloc_table BUG_ON(nents > max_ents); 438: 9a000000 bls 440 <__sg_alloc_table+0x20> 43c: eafffffe b 43c <__sg_alloc_table+0x1c> Adding volatile makes the compiler to avoid optimizations on this code, which makes the panic to occur: BUG_ON(nents > max_ents); 438: 9a000002 bls 448 <__sg_alloc_table+0x28> 43c: e3a03000 mov r3, #0 440: e5833000 str r3, [r3] 444: eafffffc b 43c <__sg_alloc_table+0x1c> Seen with gnu/linux cs arm-2010q1-202 and arm2010.09-50. Signed-off-by: Omar Ramirez Luna --- If needed I can change: ./arch/arm/mach-clps711x/include/mach/io.h: #define __raw_readsb(p,d,l) do { *(int *)0 = 0; } while (0) ./arch/arm/mach-clps711x/include/mach/io.h: #define __raw_readsl(p,d,l) do { *(int *)0 = 0; } while (0) ./arch/arm/mach-clps711x/include/mach/io.h: #define __raw_writesb(p,d,l) do { *(int *)0 = 0; } while (0) ./arch/arm/mach-clps711x/include/mach/io.h: #define __raw_writesl(p,d,l) do { *(int *)0 = 0; } while (0) ./arch/arm/kernel/traps.c: *(int *)0 = 0; arch/arm/include/asm/bug.h | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/arch/arm/include/asm/bug.h b/arch/arm/include/asm/bug.h index 4d88425..a58d863 100644 --- a/arch/arm/include/asm/bug.h +++ b/arch/arm/include/asm/bug.h @@ -12,7 +12,7 @@ extern void __bug(const char *file, int line) __attribute__((noreturn)); #else /* this just causes an oops */ -#define BUG() do { *(int *)0 = 0; } while (1) +#define BUG() do { *(volatile int *)0 = 0; } while(1) #endif -- 1.7.1