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 <redacted>
---

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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