From: Amir Goldstein <amir73il@gmail.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: linux-unionfs@vger.kernel.org
Subject: [PATCH] ovl: fix WARN_ON nlink drop to zero
Date: Mon, 23 Mar 2020 21:08:50 +0200 [thread overview]
Message-ID: <20200323190850.3091-1-amir73il@gmail.com> (raw)
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.
Detect too low i_nlink before unlink/rename and set the overlay nlink
to the upper inode nlink (minus one for an index entry).
Reported-by: Phasip <phasip@gmail.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
fs/overlayfs/util.c | 23 ++++++++++++++++++++++-
1 file changed, 22 insertions(+), 1 deletion(-)
Miklos,
This fix passed the reported reproducers (with index=off),
overlay/034 with (index=on) and overlay/034 with s/LOWER/UPPER:
-lowerdir=$OVL_BASE_SCRATCH_MNT/$OVL_LOWER
+lowerdir=$OVL_BASE_SCRATCH_MNT/$OVL_UPPER
workdir=$OVL_BASE_SCRATCH_MNT/$OVL_WORK
As well as the rest of overlay/quick group.
I will post the overlay/034 fork as a separate test later.
Thanks,
Amir.
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 36b60788ee47..e894a14857c7 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -734,7 +734,9 @@ static void ovl_cleanup_index(struct dentry *dentry)
int ovl_nlink_start(struct dentry *dentry)
{
struct inode *inode = d_inode(dentry);
+ struct inode *iupper = ovl_inode_upper(inode);
const struct cred *old_cred;
+ int index_nlink;
int err;
if (WARN_ON(!inode))
@@ -764,7 +766,26 @@ int ovl_nlink_start(struct dentry *dentry)
if (err)
return err;
- if (d_is_dir(dentry) || !ovl_test_flag(OVL_INDEX, inode))
+ if (d_is_dir(dentry))
+ goto out;
+
+ /* index adds +1 to upper nlink */
+ index_nlink = !!ovl_test_flag(OVL_INDEX, inode);
+ if (iupper && (iupper->i_nlink - index_nlink) > inode->i_nlink) {
+ pr_warn_ratelimited("inode nlink too low (%pd2, ino=%lu, nlink=%u, upper_nlink=%u)\n",
+ dentry, inode->i_ino, inode->i_nlink,
+ iupper->i_nlink - index_nlink);
+ /*
+ * Upper hardlinks were added while overlay is mounted.
+ * Unlinking all overlay hardlinks would drop overlay nlink to
+ * zero before all upper inodes are unlinked. As a safety
+ * measure, when that situation is detected, set the overlay
+ * nlink to the upper inode nlink minus one for the index entry.
+ */
+ set_nlink(d_inode(dentry), iupper->i_nlink - index_nlink);
+ }
+
+ if (!index_nlink)
goto out;
old_cred = ovl_override_creds(dentry->d_sb);
--
2.17.1
next reply other threads:[~2020-03-23 19:09 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-23 19:08 Amir Goldstein [this message]
2020-03-24 9:48 ` [PATCH] ovl: fix WARN_ON nlink drop to zero Miklos Szeredi
2020-03-24 10:20 ` Amir Goldstein
2020-03-25 10:33 ` Miklos Szeredi
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