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author | Davidlohr Bueso <dave@stgolabs.ne> | 2015-10-29 20:25:59 (GMT) |
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committer | Jens Axboe <axboe@fb.com> | 2015-10-29 20:25:59 (GMT) |
commit | cdea01b2bf98affb7e9c44530108a4a28535eee8 (patch) | |
tree | d76f70baf592052d4dff44e45bcde1ee29062570 /block/blk-mq.c | |
parent | cfd0c552a8272d691691f40073654d775836e23a (diff) | |
download | linux-cdea01b2bf98affb7e9c44530108a4a28535eee8.tar.xz |
blktrace: re-write setting q->blk_trace
This is really about simplifying the double xchg patterns into
a single cmpxchg, with the same logic. Other than the immediate
cleanup, there are some subtleties this change deals with:
(i) While the load of the old bt is fully ordered wrt everything,
ie:
old_bt = xchg(&q->blk_trace, bt); [barrier]
if (old_bt)
(void) xchg(&q->blk_trace, old_bt); [barrier]
blk_trace could still be changed between the xchg and the old_bt
load. Note that this description is merely theoretical and afaict
very small, but doing everything in a single context with cmpxchg
closes this potential race.
(ii) Ordering guarantees are obviously kept with cmpxchg.
(iii) Gets rid of the hacky-by-nature (void)xchg pattern.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
eviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block/blk-mq.c')
0 files changed, 0 insertions, 0 deletions