io_uring/cmd_net: end TX_TIMESTAMP multishot when the CQ is full

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SOCKET_URING_OP_TX_TIMESTAMP arms an EPOLLERR apoll multishot and, on
each error queue edge, posts one 32 byte aux CQE per timestamp skb. Aux
CQEs have no overflow backing, so io_uring_cmd_post_mshot_cqe32() fails
once the CQ ring is full. The loop then stops, splices the unprocessed
skbs back onto sk_error_queue and returns -EAGAIN.

-EAGAIN is IOU_RETRY, so the request goes idle until the next poll
event. io_arm_apoll() forces EPOLLET and draining the CQ does not re-run
the command, so the spliced-back timestamps stay queued until an
unrelated later timestamp produces a new edge.

End the multishot when a CQE cannot be posted, as multishot poll and
recv already do. There is no partial result to report, so complete with
-ENOBUFS: no CQ space is left for the timestamp CQEs. This command does
not use provided buffers, so the value cannot be confused with a buffer
ring running empty. The terminal CQE still reaches userspace because
request completions can go to the overflow list. The application sees a
CQE without IORING_CQE_F_MORE, which it already has to handle, and the
first issue of the re-armed request delivers the queued timestamps.

A timestamp that cannot be extracted keeps its current behaviour.

This was found with LLM assistance while reviewing io_uring multishot
handlers for the pattern behind a RECV_ZC stall reported earlier (see
Link), and confirmed with a reproducer on v7.3-rc2 and an A/B run of
this patch.

Fixes: 9e4ed359b8 ("io_uring/netcmd: add tx timestamping cmd support")
Link: https://lore.kernel.org/all/010001a0cd914529-23df2f94-bbe0-49cd-ae5d-05922356fa12-000000@email.amazonses.com/
Cc: stable@vger.kernel.org
Assisted-by: Codex:gpt-6-sol
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: lollipopkit <a@lolli.tech>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://patch.msgid.link/20260927074206.65427-1-a@lolli.tech
Signed-off-by: Jens Axboe <axboe@kernel.dk>

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lollipopkit 2026-09-27 15:42:06 +08:00 • committed by Jens Axboe

parent 98ad5b63f5

commit 3a3d93070c

1 changed files with 14 additions and 5 deletions

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io_uring/cmd_net.c

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