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| author | Jens Axboe <axboe@kernel.dk> | 2017-10-04 11:22:24 -0600 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2017-10-04 11:22:24 -0600 |
| commit | fc13457f74dcf054b0d17efb7b94b46fdf17f412 (patch) | |
| tree | b7a6a14246cf9e9c9967c7072d96a0010d117164 /block/blk-mq.c | |
| parent | a7af0af32171c17d881e3e58b0925c4a44fb5a42 (diff) | |
| download | linux-fc13457f74dcf054b0d17efb7b94b46fdf17f412.tar.gz linux-fc13457f74dcf054b0d17efb7b94b46fdf17f412.tar.bz2 linux-fc13457f74dcf054b0d17efb7b94b46fdf17f412.zip | |
blk-mq: document the need to have STARTED and COMPLETED share a byte
For memory ordering guarantees on stores, we need to ensure that
these two bits share the same byte of storage in the unsigned
long. Add a comment as to why, and a BUILD_BUG_ON() to ensure that
we don't violate this requirement.
Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-mq.c')
| -rw-r--r-- | block/blk-mq.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c index a7b46b754a7c..076cbab9c3e0 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2923,6 +2923,12 @@ EXPORT_SYMBOL_GPL(blk_mq_poll); static int __init blk_mq_init(void) { + /* + * See comment in block/blk.h rq_atomic_flags enum + */ + BUILD_BUG_ON((REQ_ATOM_STARTED / BITS_PER_BYTE) != + (REQ_ATOM_COMPLETE / BITS_PER_BYTE)); + cpuhp_setup_state_multi(CPUHP_BLK_MQ_DEAD, "block/mq:dead", NULL, blk_mq_hctx_notify_dead); return 0; |