| Message ID | 20190424215422.7404-3-source@stbuehler.de (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
| Series | [barrier,cleanup,v1,1/7] io_uring: fix notes on barriers | expand |
diff --git a/fs/io_uring.c b/fs/io_uring.c index 1f4419f38ef1..2c101230df71 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -431,8 +431,11 @@ static struct io_uring_cqe *io_get_cqring(struct io_ring_ctx *ctx) unsigned tail; tail = ctx->cached_cq_tail; - /* See comment at the top of the file */ - smp_rmb(); + /* + * writes to the cq entry need to come after reading head; the + * control dependency is enough as we're using WRITE_ONCE to + * fill the cq entry + */ if (tail - READ_ONCE(ring->r.head) == ring->ring_entries) return NULL;
The memory operations before reading cq head are unrelated and we don't care about their order. Document that the control dependency in combination with READ_ONCE and WRITE_ONCE forms a barrier we need. Signed-off-by: Stefan Bühler <source@stbuehler.de> --- fs/io_uring.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)