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io_uring/io-wq: close io-wq full-stop gap 

There is an old problem with io-wq cancellation where requests should be
killed and are in io-wq but are not discoverable, e.g. in @next_hashed
or @linked vars of io_worker_handle_work(). It adds some unreliability
to individual request canellation, but also may potentially get
__io_uring_cancel() stuck. For instance:

1) An __io_uring_cancel()'s cancellation round have not found any
   request but there are some as desribed.
2) __io_uring_cancel() goes to sleep
3) Then workers wake up and try to execute those hidden requests
   that happen to be unbound.

As we already cancel all requests of io-wq there, set IO_WQ_BIT_EXIT
in advance, so preventing 3) from executing unbound requests. The
workers will initially break looping because of getting a signal as they
are threads of the dying/exec()'ing user task.

Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/abfcf8c54cb9e8f7bfbad7e9a0cc5433cc70bdc2.1621781238.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2021-05-23 15:48:39 +01:00 committed by Jens Axboe
parent ba5ef6dc8a
commit 17a91051fe
3 changed files with 16 additions and 12 deletions
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20
fs/io-wq.c
View File

@ -979,13 +979,16 @@ static bool io_task_work_match(struct callback_head *cb, void *data)
return cwd->wqe->wq == data;
}
void io_wq_exit_start(struct io_wq *wq)
{
set_bit(IO_WQ_BIT_EXIT, &wq->state);
}
static void io_wq_exit_workers(struct io_wq *wq)
{
struct callback_head *cb;
int node;
set_bit(IO_WQ_BIT_EXIT, &wq->state);
if (!wq->task)
return;
@ -1020,8 +1023,6 @@ static void io_wq_destroy(struct io_wq *wq)
cpuhp_state_remove_instance_nocalls(io_wq_online, &wq->cpuhp_node);
io_wq_exit_workers(wq);
for_each_node(node) {
struct io_wqe *wqe = wq->wqes[node];
struct io_cb_cancel_data match = {
@ -1036,16 +1037,13 @@ static void io_wq_destroy(struct io_wq *wq)
kfree(wq);
}
void io_wq_put(struct io_wq *wq)
{
if (refcount_dec_and_test(&wq->refs))
io_wq_destroy(wq);
}
void io_wq_put_and_exit(struct io_wq *wq)
{
WARN_ON_ONCE(!test_bit(IO_WQ_BIT_EXIT, &wq->state));
io_wq_exit_workers(wq);
io_wq_put(wq);
if (refcount_dec_and_test(&wq->refs))
io_wq_destroy(wq);
}
static bool io_wq_worker_affinity(struct io_worker *worker, void *data)

2
fs/io-wq.h
View File

@ -122,7 +122,7 @@ struct io_wq_data {
};
struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data);
void io_wq_put(struct io_wq *wq);
void io_wq_exit_start(struct io_wq *wq);
void io_wq_put_and_exit(struct io_wq *wq);
void io_wq_enqueue(struct io_wq *wq, struct io_wq_work *work);

6
fs/io_uring.c
View File

@ -9078,6 +9078,9 @@ static void io_uring_cancel_sqpoll(struct io_sq_data *sqd)
if (!current->io_uring)
return;
if (tctx->io_wq)
io_wq_exit_start(tctx->io_wq);
WARN_ON_ONCE(!sqd || sqd->thread != current);
atomic_inc(&tctx->in_idle);
@ -9112,6 +9115,9 @@ void __io_uring_cancel(struct files_struct *files)
DEFINE_WAIT(wait);
s64 inflight;
if (tctx->io_wq)
io_wq_exit_start(tctx->io_wq);
/* make sure overflow events are dropped */
atomic_inc(&tctx->in_idle);
do {