ovl: fix WARN_ON nlink drop to zero (83552eac) · Commits · 戴 / test

Changes to underlying layers should not cause WARN_ON(), but this repro does: mkdir w l u mnt sudo mount -t overlay -o workdir=w,lowerdir=l,upperdir=u overlay mnt touch mnt/h ln u/h u/k rm -rf mnt/k rm -rf mnt/h dmesg ------------[ cut here ]------------ WARNING: CPU: 1 PID: 116244 at fs/inode.c:302 drop_nlink+0x28/0x40 After upper hardlinks were added while overlay is mounted, unlinking all overlay hardlinks drops overlay nlink to zero before all upper inodes are unlinked. After unlink/rename prevent i_nlink from going to zero if there are still hashed aliases (i.e. cached hard links to the victim) remaining. Reported-by:

Phasip <phasip@gmail.com> Signed-off-by:

Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/dir.c

+24 −2

Original line number	Diff line number	Diff line
		@@ -822,6 +822,28 @@ static bool ovl_pure_upper(struct dentry *dentry)
		!ovl_test_flag(OVL_WHITEOUTS, d_inode(dentry));
		}

		static void ovl_drop_nlink(struct dentry *dentry)
		{
		struct inode *inode = d_inode(dentry);
		struct dentry *alias;

		/* Try to find another, hashed alias */
		spin_lock(&inode->i_lock);
		hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
		if (alias != dentry && !d_unhashed(alias))
		break;
		}
		spin_unlock(&inode->i_lock);

		/*
		* Changes to underlying layers may cause i_nlink to lose sync with
		* reality. In this case prevent the link count from going to zero
		* prematurely.
		*/
		if (inode->i_nlink > !!alias)
		drop_nlink(inode);
		}

		static int ovl_do_remove(struct dentry *dentry, bool is_dir)
		{
		int err;
		@@ -859,7 +881,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
		if (is_dir)
		clear_nlink(dentry->d_inode);
		else
		drop_nlink(dentry->d_inode);
		ovl_drop_nlink(dentry);
		}
		ovl_nlink_end(dentry);

		@@ -1204,7 +1226,7 @@ static int ovl_rename(struct inode olddir, struct dentry old,
		if (new_is_dir)
		clear_nlink(d_inode(new));
		else
		drop_nlink(d_inode(new));
		ovl_drop_nlink(new);
		}

		ovl_dir_modified(old->d_parent, ovl_type_origin(old) \|\|

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