Re: io_uring: should IORING_TIMEOUT_ABS honour the submitter's time namespace?

[Xie Maoyi]

On <5/2/26>, Maoyi Xie wrote (correcting my own earlier reply):
> Under SQPOLL, the parse path runs in the SQPOLL kernel thread. That thread is in the initial time namespace. So timens_ktime_to_host() through "current" silently misses the offset for SQPOLL submitters.

Apologies, that paragraph in my previous reply was wrong. I have tested it.

Vanilla v7.0, SQPOLL ring inside a fresh CLONE_NEWTIME with a -10s monotonic offset, ABS deadline = now + 1s:

    [child] SQPOLL TIMEOUT_ABS elapsed=1 ms (bug fires immediately)

Same kernel with your conversion logic applied:

    [child] SQPOLL TIMEOUT_ABS elapsed=1000 ms (offset honoured)

The reason is in create_io_thread(). It is called with CLONE_THREAD and no CLONE_NEW* flag. copy_namespaces() therefore shares the submitter's nsproxy by reference rather than allocating a fresh one. Inside the SQPOLL kthread current->nsproxy->time_ns is the submitter's time_ns. timens_ktime_to_host() resolves correctly. So the SQPOLL follow-up I floated is unnecessary, your draft covers both paths.

While verifying SQPOLL, I also noticed io_uring/wait.c around lines 230-234. The IORING_ENTER_ABS_TIMER path on io_uring_enter() parses ext_arg->ts inline rather than going through io_parse_user_time, so it does not pick up your fix. Same shape of bug, separate code path. PoC on vanilla shows elapsed = 1 ms, patched shows ~1000 ms. I can send the small follow-up patch for that path as a separate thread once your IORING_OP_TIMEOUT side has landed, or fold it into the same series. Whichever you prefer.

Best regards,
Maoyi
Nanyang Technological University
https://maoyixie.com/
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