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io_uring: add memory barrier to synchronize io_kiocb's result and iopoll_completed

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In io_complete_rw_iopoll(), stores to io_kiocb's result and iopoll
completed are two independent store operations, to ensure that once
iopoll_completed is ture and then req->result must been perceived by
the cpu executing io_do_iopoll(), proper memory barrier should be used.

And in io_do_iopoll(), we check whether req->result is EAGAIN, if it is,
we'll need to issue this io request using io-wq again. In order to just
issue a single smp_rmb() on the completion side, move the re-submit work
to io_iopoll_complete().

Cc: stable@vger.kernel.org
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
[axboe: don't set ->iopoll_completed for -EAGAIN retry]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Xiaoguang Wang 2020-06-16 02:06:38 +08:00 committed by Jens Axboe
parent 2d7d67920e
commit bbde017a32
1 changed files with 29 additions and 24 deletions
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53
fs/io_uring.c
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@ -1742,6 +1742,18 @@ static int io_put_kbuf(struct io_kiocb *req)
return cflags;
}
static void io_iopoll_queue(struct list_head *again)
{
struct io_kiocb *req;
do {
req = list_first_entry(again, struct io_kiocb, list);
list_del(&req->list);
refcount_inc(&req->refs);
io_queue_async_work(req);
} while (!list_empty(again));
}
/*
* Find and free completed poll iocbs
*/
@ -1750,12 +1762,21 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
{
struct req_batch rb;
struct io_kiocb *req;
LIST_HEAD(again);
/* order with ->result store in io_complete_rw_iopoll() */
smp_rmb();
rb.to_free = rb.need_iter = 0;
while (!list_empty(done)) {
int cflags = 0;
req = list_first_entry(done, struct io_kiocb, list);
if (READ_ONCE(req->result) == -EAGAIN) {
req->iopoll_completed = 0;
list_move_tail(&req->list, &again);
continue;
}
list_del(&req->list);
if (req->flags & REQ_F_BUFFER_SELECTED)
@ -1773,18 +1794,9 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
if (ctx->flags & IORING_SETUP_SQPOLL)
io_cqring_ev_posted(ctx);
io_free_req_many(ctx, &rb);
}
static void io_iopoll_queue(struct list_head *again)
{
struct io_kiocb *req;
do {
req = list_first_entry(again, struct io_kiocb, list);
list_del(&req->list);
refcount_inc(&req->refs);
io_queue_async_work(req);
} while (!list_empty(again));
if (!list_empty(&again))
io_iopoll_queue(&again);
}
static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
@ -1792,7 +1804,6 @@ static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
{
struct io_kiocb *req, *tmp;
LIST_HEAD(done);
LIST_HEAD(again);
bool spin;
int ret;
@ -1818,13 +1829,6 @@ static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
if (!list_empty(&done))
break;
if (req->result == -EAGAIN) {
list_move_tail(&req->list, &again);
continue;
}
if (!list_empty(&again))
break;
ret = kiocb->ki_filp->f_op->iopoll(kiocb, spin);
if (ret < 0)
break;
@ -1837,9 +1841,6 @@ static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
if (!list_empty(&done))
io_iopoll_complete(ctx, nr_events, &done);
if (!list_empty(&again))
io_iopoll_queue(&again);
return ret;
}
@ -1990,10 +1991,14 @@ static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
if (res != -EAGAIN && res != req->result)
req_set_fail_links(req);
req->result = res;
if (res != -EAGAIN)
WRITE_ONCE(req->result, res);
/* order with io_poll_complete() checking ->result */
if (res != -EAGAIN) {
smp_wmb();
WRITE_ONCE(req->iopoll_completed, 1);
}
}
/*
* After the iocb has been issued, it's safe to be found on the poll list.