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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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