linux-kernel - Re: [PATCH] fuse: fix possible deadlock if rings are never initialized

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Message-ID: <CAJfpegu2ABH7dTWw4RuR79f3_e2u0D0YX8Mhjg5Gtni4PMJcMg@mail.gmail.com>
Date: Wed, 19 Mar 2025 12:42:16 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: Christian Brauner <brauner@...nel.org>
Cc: Luis Henriques <luis@...lia.com>, Bernd Schubert <bernd@...ernd.com>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kernel-dev@...lia.com
Subject: Re: [PATCH] fuse: fix possible deadlock if rings are never initialized

On Thu, 6 Mar 2025 at 12:12, Luis Henriques <luis@...lia.com> wrote:
>
> When mounting a user-space filesystem using io_uring, the initialization
> of the rings is done separately in the server side.  If for some reason
> (e.g. a server bug) this step is not performed it will be impossible to
> unmount the filesystem if there are already requests waiting.
>
> This issue is easily reproduced with the libfuse passthrough_ll example,
> if the queue depth is set to '0' and a request is queued before trying to
> unmount the filesystem.  When trying to force the unmount, fuse_abort_conn()
> will try to wake up all tasks waiting in fc->blocked_waitq, but because the
> rings were never initialized, fuse_uring_ready() will never return 'true'.
>
> Fixes: 3393ff964e0f ("fuse: block request allocation until io-uring init is complete")
> Signed-off-by: Luis Henriques <luis@...lia.com>

Acked-by: Miklos Szeredi <mszeredi@...hat.com>

Christian, can you please pick this up as well for 6.14?

Thanks,
Miklos


> ---
>  fs/fuse/dev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index 7edceecedfa5..2fe565e9b403 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -77,7 +77,7 @@ void fuse_set_initialized(struct fuse_conn *fc)
>  static bool fuse_block_alloc(struct fuse_conn *fc, bool for_background)
>  {
>         return !fc->initialized || (for_background && fc->blocked) ||
> -              (fc->io_uring && !fuse_uring_ready(fc));
> +              (fc->io_uring && fc->connected && !fuse_uring_ready(fc));
>  }
>
>  static void fuse_drop_waiting(struct fuse_conn *fc)