[Devel] [PATCH hci-8.1 3/3] fs/fuse: use wait_var_event to wait for fuse file references

[no-reply at sashiko.virtuozzo.com]

> On close_wait mounts, fuse_release_close_wait() needs to wait for all
> asynchronous references to the fuse file to be dropped before sending
> FUSE_RELEASE. This wait on fi->page_waitq was inherited from the past
> implementation and is no longer appropriate as the wait condition
> evolved:
> 
>  - fi->page_waitq is meant to serve page-under-writeback waiters and
>    fuse_set_nowrite()'s writectr waiters; now it also has to serve the
>    ff reference waiter, so every wakeup can wake unrelated waiters.
> 
>  - the wake is decoupled from the decrement, so every path dropping an
>    ff reference must remember to wake fi->page_waitq, and because of
>    this we grew two variants of the stock fuse_file_put():
>    __fuse_file_put() and fuse_release_ff(). This is bug prone, and a
>    misuse can leave the releaser blocked forever.
> 
> Instead of waiting on fi->page_waitq, a simple wait_var_event() on
> &ff->count serves the purpose best: the matching wake_up_var() uses
> the address purely as a hash key and never dereferences it, so the
> wakeup can be folded into fuse_file_put() itself. With that, both
> __fuse_file_put() and fuse_release_ff() become redundant and are
> removed. This cleanup also makes the code less divergent from
> mainline.
> 
> https://virtuozzo.atlassian.net/browse/VSTOR-147878
> 
> Signed-off-by: Liu Kui <kui.liu at virtuozzo.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20260930-close-wait-rework-v2-v1-0-f8062178544a@virtuozzo.com?part=3