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| author | Bart Van Assche <bvanassche@acm.org> | 2019-07-01 14:42:32 -0700 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2019-07-02 07:33:52 -0600 |
| commit | ecefd7958eb32602df07f12e9808598b2c2de84b (patch) | |
| tree | 789bcf30a838d99b02237568dae0b215cc13f944 /src/queue.c | |
| parent | bbb30995a0b4c9e3489aa5d66d1807425734b791 (diff) | |
| download | liburing-ecefd7958eb32602df07f12e9808598b2c2de84b.tar.gz liburing-ecefd7958eb32602df07f12e9808598b2c2de84b.tar.bz2 | |
Fix the use of memory barriers
Introduce the smp_load_acquire() and smp_store_release() macros. Fix
synchronization in io_uring_cq_advance() and __io_uring_get_cqe().
Remove a superfluous local variable, if-test and write barrier from
__io_uring_submit(). Remove a superfluous barrier from
test/io_uring_enter.c.
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Roman Penyaev <rpenyaev@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'src/queue.c')
| -rw-r--r-- | src/queue.c | 30 |
1 files changed, 8 insertions, 22 deletions
diff --git a/src/queue.c b/src/queue.c index bec363f..72b2293 100644 --- a/src/queue.c +++ b/src/queue.c @@ -77,7 +77,7 @@ static int __io_uring_submit(struct io_uring *ring, unsigned wait_nr) { struct io_uring_sq *sq = &ring->sq; const unsigned mask = *sq->kring_mask; - unsigned ktail, ktail_next, submitted, to_submit; + unsigned ktail, submitted, to_submit; unsigned flags; int ret; @@ -88,15 +88,11 @@ static int __io_uring_submit(struct io_uring *ring, unsigned wait_nr) * Fill in sqes that we have queued up, adding them to the kernel ring */ submitted = 0; - ktail = ktail_next = *sq->ktail; + ktail = *sq->ktail; to_submit = sq->sqe_tail - sq->sqe_head; while (to_submit--) { - ktail_next++; - read_barrier(); - sq->array[ktail & mask] = sq->sqe_head & mask; - ktail = ktail_next; - + ktail++; sq->sqe_head++; submitted++; } @@ -104,21 +100,11 @@ static int __io_uring_submit(struct io_uring *ring, unsigned wait_nr) if (!submitted) return 0; - if (*sq->ktail != ktail) { - /* - * First write barrier ensures that the SQE stores are updated - * with the tail update. This is needed so that the kernel - * will never see a tail update without the preceeding sQE - * stores being done. - */ - write_barrier(); - *sq->ktail = ktail; - /* - * The kernel has the matching read barrier for reading the - * SQ tail. - */ - write_barrier(); - } + /* + * Ensure that the kernel sees the SQE updates before it sees the tail + * update. + */ + smp_store_release(sq->ktail, ktail); flags = 0; if (wait_nr || sq_ring_needs_enter(ring, &flags)) { |