Re: [PATCH v2 0/2] fuse: add timeout option for requests

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On Tue, Aug 6, 2024 at 10:11 AM Bernd Schubert
<bernd.schubert@xxxxxxxxxxx> wrote:
>
> On 8/6/24 18:23, Joanne Koong wrote:
>
> >>
> >> This is very interesting. These logs (and the ones above with the
> >> lxcfs server running concurrently) are showing that the read request
> >> was freed but not through the do_fuse_request_end path. It's weird
> >> that fuse_simple_request reached fuse_put_request without
> >> do_fuse_request_end having been called (which is the only place where
> >> FR_FINISHED gets set and wakes up the wait events in
> >> request_wait_answer).
> >>
> >> I'll take a deeper look tomorrow and try to make more sense of it.
> >
> > Finally realized what's happening!
> > When we kill the cat program, if the request hasn't been sent out to
> > userspace yet when the fatal signal interrupts the
> > wait_event_interruptible and wait_event_killable in
> > request_wait_answer(), this will clean up the request manually (not
> > through the fuse_request_end() path), which doesn't delete the timer.
> >
> > I'll fix this for v3.
> >
> > Thank you for surfacing this and it would be much appreciated if you
> > could test out v3 when it's submitted to make sure.
>
> It is still just a suggestion, but if the timer would have its own ref,
> any oversight of another fuse_put_request wouldn't be fatal.
>

Thanks for the suggestion. My main concerns are whether it's worth the
extra (minimal?) performance penalty for something that's not strictly
needed and whether it ends up adding more of a burden to keep track of
the timer ref (eg in error handling like the case above where the
fatal signal is for a request that hasn't been sent to userspace yet,
having to account for the extra timer ref if the timer callback didn't
execute). I don't think adding a timer ref would prevent fatal crashes
on fuse_put_request oversights (unless we also mess up not releasing a
corresponding timer ref  :))

I don't feel that strongly about this though so if you do, I can add
this in for v3.

Thanks,
Joanne

>
> Thanks,
> Bernd





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