5.15-stable review patch. If anyone has any objections, please let me know.
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From: Pavel Begunkov asml.silence@gmail.com
commit f8b632e89a101dae349a7b212c1771d7925f441b upstream.
io_uring_cancel_generic() should retry if any state changes like a request is completed, however in case of a task exit it only goes for another loop and avoids schedule() if any tracked (i.e. REQ_F_INFLIGHT) request got completed.
Let's assume we have a non-tracked request executing in iowq and a tracked request linked to it. Let's also assume io_uring_cancel_generic() fails to find and cancel the request, i.e. via io_run_local_work(), which may happen as io-wq has gaps. Next, the request logically completes, io-wq still hold a ref but queues it for completion via tw, which happens in io_uring_try_cancel_requests(). After, right before prepare_to_wait() io-wq puts the request, grabs the linked one and tries executes it, e.g. arms polling. Finally the cancellation loop calls prepare_to_wait(), there are no tw to run, no tracked request was completed, so the tctx_inflight() check passes and the task is put to indefinite sleep.
Cc: stable@vger.kernel.org Fixes: 3f48cf18f886c ("io_uring: unify files and task cancel") Signed-off-by: Pavel Begunkov asml.silence@gmail.com Link: https://lore.kernel.org/r/acac7311f4e02ce3c43293f8f1fda9c705d158f1.172181938... Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- io_uring/io_uring.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -9856,8 +9856,11 @@ static void io_uring_cancel_generic(bool atomic_inc(&tctx->in_idle); do { io_uring_drop_tctx_refs(current); + if (!tctx_inflight(tctx, !cancel_all)) + break; + /* read completions before cancelations */ - inflight = tctx_inflight(tctx, !cancel_all); + inflight = tctx_inflight(tctx, false); if (!inflight) break;