releases/4.16.4/block-use-32-bit-blk_status_t-on-alpha.patch

   1 From 6e2fb22103b99c26ae30a46512abe75526d8e4c9 Mon Sep 17 00:00:00 2001
   2 From: Mikulas Patocka <mpatocka@redhat.com>
   3 Date: Wed, 21 Mar 2018 12:42:25 -0400
   4 Subject: block: use 32-bit blk_status_t on Alpha
   5
   6 From: Mikulas Patocka <mpatocka@redhat.com>
   7
   8 commit 6e2fb22103b99c26ae30a46512abe75526d8e4c9 upstream.
   9
  10 Early alpha processors cannot write a single byte or word; they read 8
  11 bytes, modify the value in registers and write back 8 bytes.
  12
  13 The type blk_status_t is defined as one byte, it is often written
  14 asynchronously by I/O completion routines, this asynchronous modification
  15 can corrupt content of nearby bytes if these nearby bytes can be written
  16 simultaneously by another CPU.
  17
  18 - one example of such corruption is the structure dm_io where
  19   "blk_status_t status" is written by an asynchronous completion routine
  20   and "atomic_t io_count" is modified synchronously
  21 - another example is the structure dm_buffer where "unsigned hold_count"
  22   is modified synchronously from process context and "blk_status_t
  23   write_error" is modified asynchronously from bio completion routine
  24
  25 This patch fixes the bug by changing the type blk_status_t to 32 bits if
  26 we are on Alpha and if we are compiling for a processor that doesn't have
  27 the byte-word-extension.
  28
  29 Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
  30 Cc: stable@vger.kernel.org      # 4.13+
  31 Signed-off-by: Jens Axboe <axboe@kernel.dk>
  32 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  33
  34 ---
  35  include/linux/blk_types.h |    5 +++++
  36  1 file changed, 5 insertions(+)
  37
  38 --- a/include/linux/blk_types.h
  39 +++ b/include/linux/blk_types.h
  40 @@ -20,8 +20,13 @@ typedef void (bio_end_io_t) (struct bio
  41
  42  /*
  43   * Block error status values.  See block/blk-core:blk_errors for the details.
  44 + * Alpha cannot write a byte atomically, so we need to use 32-bit value.
  45   */
  46 +#if defined(CONFIG_ALPHA) && !defined(__alpha_bwx__)
  47 +typedef u32 __bitwise blk_status_t;
  48 +#else
  49  typedef u8 __bitwise blk_status_t;
  50 +#endif
  51  #define        BLK_STS_OK 0
  52  #define BLK_STS_NOTSUPP                ((__force blk_status_t)1)
  53  #define BLK_STS_TIMEOUT                ((__force blk_status_t)2)