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    Subject[PATCH 4.16 083/196] block: use 32-bit blk_status_t on Alpha
    4.16-stable review patch.  If anyone has any objections, please let me know.


    From: Mikulas Patocka <>

    commit 6e2fb22103b99c26ae30a46512abe75526d8e4c9 upstream.

    Early alpha processors cannot write a single byte or word; they read 8
    bytes, modify the value in registers and write back 8 bytes.

    The type blk_status_t is defined as one byte, it is often written
    asynchronously by I/O completion routines, this asynchronous modification
    can corrupt content of nearby bytes if these nearby bytes can be written
    simultaneously by another CPU.

    - one example of such corruption is the structure dm_io where
    "blk_status_t status" is written by an asynchronous completion routine
    and "atomic_t io_count" is modified synchronously
    - another example is the structure dm_buffer where "unsigned hold_count"
    is modified synchronously from process context and "blk_status_t
    write_error" is modified asynchronously from bio completion routine

    This patch fixes the bug by changing the type blk_status_t to 32 bits if
    we are on Alpha and if we are compiling for a processor that doesn't have
    the byte-word-extension.

    Signed-off-by: Mikulas Patocka <>
    Cc: # 4.13+
    Signed-off-by: Jens Axboe <>
    Signed-off-by: Greg Kroah-Hartman <>

    include/linux/blk_types.h | 5 +++++
    1 file changed, 5 insertions(+)

    --- a/include/linux/blk_types.h
    +++ b/include/linux/blk_types.h
    @@ -20,8 +20,13 @@ typedef void (bio_end_io_t) (struct bio

    * Block error status values. See block/blk-core:blk_errors for the details.
    + * Alpha cannot write a byte atomically, so we need to use 32-bit value.
    +#if defined(CONFIG_ALPHA) && !defined(__alpha_bwx__)
    +typedef u32 __bitwise blk_status_t;
    typedef u8 __bitwise blk_status_t;
    #define BLK_STS_OK 0
    #define BLK_STS_NOTSUPP ((__force blk_status_t)1)
    #define BLK_STS_TIMEOUT ((__force blk_status_t)2)

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