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

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Message-ID: <20250306111218.13734-1-luis@igalia.com>
Date: Thu,  6 Mar 2025 11:12:18 +0000
From: Luis Henriques <luis@...lia.com>
To: Miklos Szeredi <miklos@...redi.hu>,
	Bernd Schubert <bernd@...ernd.com>
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	kernel-dev@...lia.com,
	Luis Henriques <luis@...lia.com>
Subject: [PATCH] fuse: fix possible deadlock if rings are never initialized

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)