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    Subject[PATCH] mtd: Fix bug using smp_processor_id() in preemptible ubi_bgt1d kthread
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    mtd: Fix bug using smp_processor_id() in preemptible ubi_bgt1d kthread

    On a MIPS Cavium Octeon CN5020 when trying to create a UBI volume,
    on the NOR flash, the kernel thread ubi_bgt1d calls
    cfi_amdstd_write_buffers() --> do_write_buffer() -->
    INVALIDATE_CACHE_UDELAY --> __udelay(). Its __udelay() that calls
    smp_processor_id() in preemptible code, which you are not supposed to.
    Fix the problem by disabling preemption.

    The kernel error messages seen when trying to create UBI volume is
    BUG: using smp_processor_id() in preemptible [00000000] code: ubi_bgt1d/843
    caller is __udelay+0x14/0x70
    Call Trace:
    [<ffffffff8110b0d4>] dump_stack+0x8/0x34
    [<ffffffff812ee1ac>] debug_smp_processor_id+0x114/0x130
    [<ffffffff812e9274>] __udelay+0x14/0x70
    [<ffffffff81337c0c>] cfi_amdstd_write_buffers+0xa9c/0xd70
    [<ffffffff8134cab0>] ubi_io_sync_erase+0x248/0x390
    [<ffffffff8134d714>] erase_worker+0x6c/0x4f8
    [<ffffffff8134e4fc>] do_work+0xac/0x138
    [<ffffffff8134e6a0>] ubi_thread+0x118/0x1a8
    [<ffffffff8115ebe0>] kthread+0x88/0x90
    [<ffffffff81115650>] kernel_thread_helper+0x10/0x18

    Signed-off-by: Philby John <pjohn@mvista.com>
    ---
    include/linux/mtd/cfi.h | 2 ++
    1 files changed, 2 insertions(+), 0 deletions(-)

    diff --git a/include/linux/mtd/cfi.h b/include/linux/mtd/cfi.h
    index 574d9ee..9673213 100644
    --- a/include/linux/mtd/cfi.h
    +++ b/include/linux/mtd/cfi.h
    @@ -495,7 +495,9 @@ static inline void cfi_udelay(int us)
    if (us >= 1000) {
    msleep((us+999)/1000);
    } else {
    + preempt_disable();
    udelay(us);
    + preempt_enable();
    cond_resched();
    }
    }
    --
    1.6.3.3.333.g4d53f




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