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Linus Torvalds
035d80695f
Pull umount fix from Al Viro:
"Brown paperbag time: dumb braino in the series that went into 5.7
broke the 'don't step into ->d_weak_revalidate() when umount(2) looks
the victim up' behaviour.
Spotted only now - saw
if (!err && unlikely(nd->flags & LOOKUP_MOUNTPOINT)) {
err = handle_lookup_down(nd);
nd->flags &= ~LOOKUP_JUMPED; // no d_weak_revalidate(), please...
}
and went "why do we clear that flag here - nothing below that point is
going to check it anyway" / "wait a minute, what is it doing *after*
complete_walk() (which is where we check that flag and call
->d_weak_revalidate())" / "how could that possibly _not_ break?",
followed by reproducing the breakage and verifying that the obvious
fix of that braino does, indeed, fix it.
The reproducer is (assuming that $DIR exists and is exported r/w to
localhost)
mkdir $DIR/a
mkdir /tmp/foo
mount --bind /tmp/foo /tmp/foo
mkdir /tmp/foo/a
mkdir /tmp/foo/b
mount -t nfs4 localhost:$DIR/a /tmp/foo/a
mount -t nfs4 localhost:$DIR /tmp/foo/b
rmdir /tmp/foo/b/a
umount /tmp/foo/b
umount /tmp/foo/a
umount -l /tmp/foo # will get everything under /tmp/foo, no matter what
Correct behaviour is successful umount; broken kernels (5.7-rc1 and
later) get
umount.nfs4: /tmp/foo/a: Stale file handle
Note that bind mount is there to be able to recover - on broken
kernels we'd get stuck with impossible-to-umount filesystem if not for
that.
FWIW, that braino had been posted for review back then, at least
twice. Unfortunately, the call of complete_walk() was outside of diff
context, so the bogosity hadn't been immediately obvious from the
patch alone ;-/"
* 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
LOOKUP_MOUNTPOINT: we are cleaning "jumped" flag too late
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