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fuse: Fix the condition to enable over-io-uring

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The existing condition in fuse_uring_cmd() is there only to avoid
disabling io-uring for connections that already run with it, missing
was a condition to refuse any IORING_OP_URING_CMD if the
connection/channel didn't get enabled because of missing FUSE_INIT
reply flag FUSE_OVER_IO_URING. Without the reply flag the barrier in
fuse_uring_ready() doesn't work and IO could already be going on and
cause deadlock states (at a minimum one between fch->bg_lock and
queue->lock).

The change itself is trivial, but brings behavior change,
FUSE_OVER_IO_URING has to be set in the FUSE_INIT_REPLY by fuse servers
to accept any IORING_OP_URING_CMD. Libfuse does that and the only
non-libfuse implementation I found (fractal-fuse) also does it.
Qemu patches for fuse-io-uring are not merged yet, as far as I know.

Moved up is the smp_load_acquire(&fch->initialized) check, as a
fuse-server implementation might try to setup io-uring before FUSE_INIT
is processed and might have gotten -EOPNOTSUPP instead of -EAGAIN.

Also fixed is a stale comment that explains the handling of the
FUSE_OVER_IO_URING flag in early RFC versions.

If there should be a report from any library or application we
probably need to revert this commit.

Fixes: 3393ff964e ("fuse: block request allocation until io-uring init is complete")
Signed-off-by: Bernd Schubert <bernd@bsbernd.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Bernd Schubert
2026-08-21 18:19:09 +02:00
committed by Miklos Szeredi
parent 26d7e1f5c4
commit 1f59015e95
2 changed files with 18 additions and 17 deletions
Download Patch File Download Diff File Expand all files Collapse all files

31
fs/fuse/dev_uring.c
View File

@@ -1665,25 +1665,30 @@ int fuse_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
}
fch = fud->chan;
/* Once a connection has io-uring enabled on it, it can't be disabled */
if (!enable_uring && !fch->io_uring) {
pr_info_ratelimited("fuse-io-uring is disabled\n");
return -EOPNOTSUPP;
}
/*
* The ring is sized from values negotiated by FUSE_INIT
*
* Pairs with smp_store_release() in fuse_chan_set_initialized()
*/
if (!smp_load_acquire(&fch->initialized))
return -EAGAIN;
if (fch->abort_with_err)
return -ECONNABORTED;
if (!fch->connected)
return -ENOTCONN;
/*
* fuse_uring_register() needs the ring to be initialized,
* we need to know the max payload size
*
* Pairs with smp_store_release() in fuse_chan_set_initialized()
*/
if (!smp_load_acquire(&fch->initialized))
return -EAGAIN;
/* Once a connection has io-uring enabled on it, it can't be disabled */
if (!enable_uring && !fch->io_uring) {
pr_info_ratelimited("fuse-io-uring is disabled by module parameter\n");
return -EOPNOTSUPP;
}
if (!fch->io_uring) {
pr_info_ratelimited(
"fuse-io-uring not enabled on this connection\n");
return -EOPNOTSUPP;
}
switch (cmd_op) {
case FUSE_IO_URING_CMD_REGISTER:

4
fs/fuse/inode.c
View File

@@ -1480,10 +1480,6 @@ static struct fuse_init_args *fuse_new_init(struct fuse_mount *fm)
if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
flags |= FUSE_PASSTHROUGH;
/*
* This is just an information flag for fuse server. No need to check
* the reply - server is either sending IORING_OP_URING_CMD or not.
*/
if (fuse_uring_enabled())
flags |= FUSE_OVER_IO_URING | FUSE_HAS_IO_URING_BUFPOOL;