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io_uring: don't enter poll loop if we have CQEs pending

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We need to check if we have CQEs pending before starting a poll loop,
as those could be the events we will be spinning for (and hence we'll
find none). This can happen if a CQE triggers an error, or if it is
found by eg an IRQ before we get a chance to find it through polling.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2019-08-20 11:03:11 -06:00
parent cb32de1b7e
commit a3a0e43fd7
1 changed files with 15 additions and 7 deletions
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22
fs/io_uring.c
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@ -679,6 +679,13 @@ static void io_put_req(struct io_kiocb *req)
io_free_req(req); io_free_req(req);
} }
static unsigned io_cqring_events(struct io_cq_ring *ring)
{
/* See comment at the top of this file */
smp_rmb();
return READ_ONCE(ring->r.tail) - READ_ONCE(ring->r.head);
}
/* /*
* Find and free completed poll iocbs * Find and free completed poll iocbs
*/ */
@ -818,6 +825,14 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, unsigned *nr_events,
do { do {
int tmin = 0; int tmin = 0;
/*
* Don't enter poll loop if we already have events pending.
* If we do, we can potentially be spinning for commands that
* already triggered a CQE (eg in error).
*/
if (io_cqring_events(ctx->cq_ring))
break;
/* /*
* If a submit got punted to a workqueue, we can have the * If a submit got punted to a workqueue, we can have the
* application entering polling for a command before it gets * application entering polling for a command before it gets
@ -2449,13 +2464,6 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
return submit; return submit;
} }
static unsigned io_cqring_events(struct io_cq_ring *ring)
{
/* See comment at the top of this file */
smp_rmb();
return READ_ONCE(ring->r.tail) - READ_ONCE(ring->r.head);
}
/* /*
* Wait until events become available, if we don't already have some. The * Wait until events become available, if we don't already have some. The
* application must reap them itself, as they reside on the shared cq ring. * application must reap them itself, as they reside on the shared cq ring.