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propagate_umount(): only surviving overmounts should be reparented

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... as the comments in reparent() clearly say.  As it is, we reparent
*all* overmounts of the mounts being taken out, including those that
are taken out themselves.  It's not only a potentially massive slowdown
(on a pathological setup we might end up with O(N^2) time for N mounts
being kicked out), it can end up with incorrect ->overmount in the
surviving mounts.

Fixes: f0d0ba1998 "Rewrite of propagate_umount()"
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2025-08-14 23:32:26 -04:00
parent 0ddfb62f5d
commit da025cdb97
1 changed files with 4 additions and 3 deletions
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7
fs/pnode.c
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@@ -637,10 +637,11 @@ void propagate_umount(struct list_head *set)
}
// now to_umount consists of all acceptable candidates
// deal with reparenting of remaining overmounts on those
// deal with reparenting of surviving overmounts on those
list_for_each_entry(m, &to_umount, mnt_list) {
if (m->overmount)
reparent(m->overmount);
struct mount *over = m->overmount;
if (over && !will_be_unmounted(over))
reparent(over);
}
// and fold them into the set