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io_uring: recycle provided before arming poll

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We currently have a race where we recycle the selected buffer if poll
returns IO_APOLL_OK. But that's too late, as the poll could already be
triggering or have triggered. If that race happens, then we're putting a
buffer that's already being used.

Fix this by recycling before we arm poll. This does mean that we'll
sometimes almost instantly re-select the buffer, but it's rare enough in
testing that it should not pose a performance issue.

Fixes: b1c6264575 ("io_uring: recycle provided buffers if request goes async")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2022-03-19 18:04:41 -06:00
parent 5e92936746
commit abdad709ed
1 changed files with 2 additions and 1 deletions
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3
fs/io_uring.c
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@ -6240,6 +6240,8 @@ static int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags)
req->flags |= REQ_F_POLLED;
ipt.pt._qproc = io_async_queue_proc;
io_kbuf_recycle(req);
ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask);
if (ret || ipt.error)
return ret ? IO_APOLL_READY : IO_APOLL_ABORTED;
@ -7491,7 +7493,6 @@ static void io_queue_sqe_arm_apoll(struct io_kiocb *req)
io_queue_async_work(req, NULL);
break;
case IO_APOLL_OK:
io_kbuf_recycle(req);
break;
}