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fuse: fix missing barrier when checking io-uring readiness

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fuse_block_alloc() reads fch->initialized and then fch->io_uring.
fch->io_uring is set before fch->initialized, ordered by the smp_wmb()
in fuse_chan_set_intialized(), but fuse_block_alloc() has no matching
read barrier between the two loads.

This may lead a CPU to observe fch->initialized=1 but fch->io_uring=0,
and skip the check that blocks request allocation until the io-uring
queues are ready. This can reintroduce the lock-order inversion deadlock
that commit 3393ff964e prevents.

Add an smp_rmb() barrier to pair with the smp_wmb() in
fuse_chan_set_initialized() to prevent this.

Fixes: 3393ff964e ("fuse: block request allocation until io-uring init is complete")
Cc: stable@vger.kernel.org
Reviewed-by: Bernd Schubert <bernd@bsbernd.com>
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Joanne Koong
2026-07-16 11:31:42 -07:00
committed by Miklos Szeredi
parent ed9c881f3b
commit edb310bc27
1 changed files with 7 additions and 4 deletions
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11
fs/fuse/dev.c
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@@ -85,7 +85,13 @@ void fuse_chan_set_initialized(struct fuse_chan *fch, struct fuse_chan_param *pa
static bool fuse_block_alloc(struct fuse_chan *fch, bool for_background)
{
return !fch->initialized || (for_background && fch->blocked) ||
if (!fch->initialized)
return true;
/* Pairs with smp_wmb() in fuse_chan_set_initialized() */
smp_rmb();
return (for_background && fch->blocked) ||
(fch->io_uring && fch->connected && !fuse_uring_ready(fch));
}
@@ -120,9 +126,6 @@ static struct fuse_req *fuse_get_req(struct fuse_chan *fch, bool for_background)
goto out;
}
/* Matches smp_wmb() in fuse_chan_set_initialized() */
smp_rmb();
err = -ENOTCONN;
if (!fch->connected)
goto out;