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io_uring: tighten task exit cancellations
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: 3f48cf1 ("io_uring: unify files and task cancel") Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> Link: https://lore.kernel.org/r/acac7311f4e02ce3c43293f8f1fda9c705d158f1.1721819383.git.asml.silence@gmail.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
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io_uring/io_uring.c

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3031,8 +3031,11 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd)
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bool loop = false;
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io_uring_drop_tctx_refs(current);
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if (!tctx_inflight(tctx, !cancel_all))
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break;
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/* read completions before cancelations */
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inflight = tctx_inflight(tctx, !cancel_all);
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inflight = tctx_inflight(tctx, false);
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if (!inflight)
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break;
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