The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y git checkout FETCH_HEAD git cherry-pick -x 56094ad3eaa21e6621396cc33811d8f72847a834 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025102042-tactical-subtract-5775@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 56094ad3eaa21e6621396cc33811d8f72847a834 Mon Sep 17 00:00:00 2001 From: Jan Kara jack@suse.cz Date: Thu, 2 Oct 2025 17:55:07 +0200 Subject: [PATCH] vfs: Don't leak disconnected dentries on umount
When user calls open_by_handle_at() on some inode that is not cached, we will create disconnected dentry for it. If such dentry is a directory, exportfs_decode_fh_raw() will then try to connect this dentry to the dentry tree through reconnect_path(). It may happen for various reasons (such as corrupted fs or race with rename) that the call to lookup_one_unlocked() in reconnect_one() will fail to find the dentry we are trying to reconnect and instead create a new dentry under the parent. Now this dentry will not be marked as disconnected although the parent still may well be disconnected (at least in case this inconsistency happened because the fs is corrupted and .. doesn't point to the real parent directory). This creates inconsistency in disconnected flags but AFAICS it was mostly harmless. At least until commit f1ee616214cb ("VFS: don't keep disconnected dentries on d_anon") which removed adding of most disconnected dentries to sb->s_anon list. Thus after this commit cleanup of disconnected dentries implicitely relies on the fact that dput() will immediately reclaim such dentries. However when some leaf dentry isn't marked as disconnected, as in the scenario described above, the reclaim doesn't happen and the dentries are "leaked". Memory reclaim can eventually reclaim them but otherwise they stay in memory and if umount comes first, we hit infamous "Busy inodes after unmount" bug. Make sure all dentries created under a disconnected parent are marked as disconnected as well.
Reported-by: syzbot+1d79ebe5383fc016cf07@syzkaller.appspotmail.com Fixes: f1ee616214cb ("VFS: don't keep disconnected dentries on d_anon") CC: stable@vger.kernel.org Signed-off-by: Jan Kara jack@suse.cz Signed-off-by: Christian Brauner brauner@kernel.org
diff --git a/fs/dcache.c b/fs/dcache.c index a067fa0a965a..035cccbc9276 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2557,6 +2557,8 @@ struct dentry *d_alloc_parallel(struct dentry *parent, spin_lock(&parent->d_lock); new->d_parent = dget_dlock(parent); hlist_add_head(&new->d_sib, &parent->d_children); + if (parent->d_flags & DCACHE_DISCONNECTED) + new->d_flags |= DCACHE_DISCONNECTED; spin_unlock(&parent->d_lock);
retry: