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Subject[PATCH] ARM: BUG() dies silently
Date
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 <omar.ramirez@ti.com>
---
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


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