Re: [RFC PATCH v2] fuse: fix race in fuse_notify_store()

[Miklos Szeredi]

On Thu, 30 Jan 2025 at 11:16, Luis Henriques <luis@xxxxxxxxxx> wrote:
>
> Userspace filesystems can push data for a specific inode without it being
> explicitly requested.  This can be accomplished by using NOTIFY_STORE.
> However, this may race against another process performing different
> operations on the same inode.
>
> If, for example, there is a process reading from it, it may happen that it
> will block waiting for data to be available (locking the folio), while the
> FUSE server will also block trying to lock the same folio to update it with
> the inode data.
>
> The easiest solution, as suggested by Miklos, is to allow the userspace
> filesystem to skip locked folios.

Not sure.

The easiest solution is to make the server perform the two operations
independently.  I.e. never trigger a notification from a request.

This is true of other notifications, e.g. doing FUSE_NOTIFY_DELETE
during e.g. FUSE_RMDIR will deadlock on i_mutex.

Or am I misunderstanding the problem?

Thanks,
Miklos