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Subject[PATCH] mtd: Fix bug using smp_processor_id() in preemptible ubi_bgt1d kthread
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 <>
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) {
} else {
+ preempt_disable();
+ preempt_enable();

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