Re: [PATCH RFC v5 15/16] fuse: {io-uring} Prevent mount point hang on fuse-server termination

[Bernd Schubert <bernd.schubert@fastmail.fm>]

On 11/18/24 20:32, Joanne Koong wrote:
> On Thu, Nov 7, 2024 at 9:04 AM Bernd Schubert <bschubert@ddn.com> wrote:
>>
>> When the fuse-server terminates while the fuse-client or kernel
>> still has queued URING_CMDs, these commands retain references
>> to the struct file used by the fuse connection. This prevents
>> fuse_dev_release() from being invoked, resulting in a hung mount
>> point.
> 
> Could you explain the flow of what happens after a fuse server
> terminates? How does that trigger the IO_URING_F_CANCEL uring cmd?

This is all about daemon termination, when the mount point is still
alive. Basically without this patch even plain (non forced umount)
hangs.
Without queued IORING_OP_URING_CMDs there is a call into 
fuse_dev_release() on daemon termination, with queued
IORING_OP_URING_CMDs this doesn't happen as each of these commands
holds a file reference.

IO_URING_F_CANCEL is triggered from from io-uring, I guess when
the io-uring file descriptor is released 
(note: 'io-uring fd' != '/dev/fuse fd').


I guess I need to improve the commit message a bit.



Cheers,
Bernd