From 0ddfb62f5d018edcb571a3d8ea30ad5332cf2a69 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Fri, 15 Aug 2025 15:38:14 -0400 Subject: [PATCH] fix the softlockups in attach_recursive_mnt() In case when we mounting something on top of a large stack of overmounts, all of them being peers of each other, we get quadratic time by the depth of overmount stack. Easily fixed by doing commit_tree() before reparenting the overmount; simplifies commit_tree() as well - it doesn't need to skip the already mounted stuff that had been reparented on top of the new mounts. Since we are holding mount_lock through both reparenting and call of commit_tree(), the order does not matter from the mount hash point of view. Reported-by: "Lai, Yi" Tested-by: "Lai, Yi" Reviewed-by: Christian Brauner Fixes: 663206854f02 "copy_tree(): don't link the mounts via mnt_list" Signed-off-by: Al Viro --- fs/namespace.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index ddfd4457d338..1c97f93d1865 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1197,10 +1197,7 @@ static void commit_tree(struct mount *mnt) if (!mnt_ns_attached(mnt)) { for (struct mount *m = mnt; m; m = next_mnt(m, mnt)) - if (unlikely(mnt_ns_attached(m))) - m = skip_mnt_tree(m); - else - mnt_add_to_ns(n, m); + mnt_add_to_ns(n, m); n->nr_mounts += n->pending_mounts; n->pending_mounts = 0; } @@ -2704,6 +2701,7 @@ static int attach_recursive_mnt(struct mount *source_mnt, lock_mnt_tree(child); q = __lookup_mnt(&child->mnt_parent->mnt, child->mnt_mountpoint); + commit_tree(child); if (q) { struct mountpoint *mp = root.mp; struct mount *r = child; @@ -2713,7 +2711,6 @@ static int attach_recursive_mnt(struct mount *source_mnt, mp = shorter; mnt_change_mountpoint(r, mp, q); } - commit_tree(child); } unpin_mountpoint(&root); unlock_mount_hash(); -- 2.25.1