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io_uring/cancel: recognize "no timeout" on 32-bit

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IORING_REGISTER_SYNC_CANCEL waits without a limit if both fields of
io_uring_sync_cancel_reg::timeout are -1. io_sync_cancel() compares them
with -1UL. They are of type long long. With a long of 32 bits -1UL is
4294967295, which is what it stays when it is converted for the
comparison, and the fields are never equal to it.

So { -1, -1 } is taken for a timeout. ktime_set() takes the nanoseconds as
an unsigned long, so what becomes of it is -1s + 4294967295ns = 3.29s.

If the request is being run by io-wq and can't be interrupted, the call
returns -ETIME after that time, rather than waiting for the request to be
gone. On i386, with a buffered read from a null_blk device that takes 4s
to complete a request, IOSQE_ASYNC, that is what each call does.

Fixes: 78a861b949 ("io_uring: add sync cancelation API through io_uring_register()")
Assisted-by: LLM
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Link: https://patch.msgid.link/20261015-b4-io-uring-fixes-v1-17-c1556f5d7bf5@toxicpanda.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Josef Bacik 2026-10-15 19:30:41 +00:00 committed by Jens Axboe
parent 8aa0e5db48
commit 3774e4d4c8
1 changed files with 1 additions and 1 deletions
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2
io_uring/cancel.c
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@ -319,7 +319,7 @@ int io_sync_cancel(struct io_ring_ctx *ctx, void __user *arg)
if (ret != -EALREADY)
goto out;
if (sc.timeout.tv_sec != -1UL || sc.timeout.tv_nsec != -1UL) {
if (sc.timeout.tv_sec != -1 || sc.timeout.tv_nsec != -1) {
struct timespec64 ts = {
.tv_sec = sc.timeout.tv_sec,
.tv_nsec = sc.timeout.tv_nsec