block: use 32-bit blk_status_t on Alpha

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 <mpatocka@redhat.com>
Cc: stable@vger.kernel.org	# 4.13+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Mikulas Patocka 2018-03-21 12:42:25 -04:00 committed by Jens Axboe
parent 818e0fa293
commit 6e2fb22103
1 changed files with 5 additions and 0 deletions

View File

@ -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;
#else
typedef u8 __bitwise blk_status_t;
#endif
#define BLK_STS_OK 0
#define BLK_STS_NOTSUPP ((__force blk_status_t)1)
#define BLK_STS_TIMEOUT ((__force blk_status_t)2)