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Subject[PATCH 1/1] io_uring: fix overflowed reqs cancellation
Date
Overflowed requests in io_uring_cancel_files() should be shed only of
inflight and overflowed refs. All other left references are owned by
someone else. E.g. a submission ref owned by __io_queue_sqe() but not
yet reached the point of releasing it.

However, if an overflowed request in io_uring_cancel_files() had extra
refs, after refcount_sub_and_test(2) check fails, it

- tries to cancel the req, which is already going away. That's pointless,
just go for the next lap of inflight waiting.

- io_put_req() underflowing req->refs of a potentially freed request.

Fixes: 2ca10259b418 ("io_uring: prune request from overflow list on flush")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/io_uring.c | 16 +++++-----------
1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index de6547e68626..01851a74bb12 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7483,19 +7483,13 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx,
WRITE_ONCE(ctx->rings->cq_overflow,
atomic_inc_return(&ctx->cached_cq_overflow));

- /*
- * Put inflight ref and overflow ref. If that's
- * all we had, then we're done with this request.
- */
- if (refcount_sub_and_test(2, &cancel_req->refs)) {
- io_free_req(cancel_req);
- finish_wait(&ctx->inflight_wait, &wait);
- continue;
- }
+ /* Put inflight ref and overflow ref. */
+ io_double_put_req(cancel_req);
+ } else {
+ io_wq_cancel_work(ctx->io_wq, &cancel_req->work);
+ io_put_req(cancel_req);
}

- io_wq_cancel_work(ctx->io_wq, &cancel_req->work);
- io_put_req(cancel_req);
schedule();
finish_wait(&ctx->inflight_wait, &wait);
}
--
2.24.0
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