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

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Message-ID: <1dc28f9d-c453-42f4-8edb-1d5c8084d576@bsbernd.com>
Date: Thu, 6 Mar 2025 12:45:59 +0100
From: Bernd Schubert <bernd@...ernd.com>
To: Luis Henriques <luis@...lia.com>, Miklos Szeredi <miklos@...redi.hu>
Cc: 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 3/6/25 12:12, Luis Henriques 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>
> ---
>  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)
> 

Oh yes, I had missed that.

Reviewed-by: Bernd Schubert <bschubert@....com>