Re: [PATCH] ovl: skip stale entries in merge dir cache iteration

[Amir Goldstein <amir73il@gmail.com>]

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On Tue, Jul 20, 2021 at 5:55 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Tue, Jul 20, 2021 at 10:18 AM Amir Goldstein <amir73il@gmail.com> wrote:
> >
> > On Tue, Jul 20, 2021 at 7:22 AM Miklos Szeredi <miklos@szeredi.hu> wrote:
> > >
> > > On Tue, 20 Jul 2021 at 06:19, Miklos Szeredi <miklos@szeredi.hu> wrote:
> > > >
> > > > On Mon, 19 Jul 2021 at 18:43, Amir Goldstein <amir73il@gmail.com> wrote:
> > > > >
> > > > > On Mon, Jul 19, 2021 at 6:24 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
> > > > > >
> > > > > > On Fri, 4 Jun 2021 at 12:43, Amir Goldstein <amir73il@gmail.com> wrote:
> > > > > > >
> > > > > > > On Mon, Apr 26, 2021 at 6:20 PM Amir Goldstein <amir73il@gmail.com> wrote:
> > > > > > > >
> > > > > > > > On the first getdents call, ovl_iterate() populates the readdir cache
> > > > > > > > with a list of entries, but for upper entries with origin lower inode,
> > > > > > > > p->ino remains zero.
> > > > > > > >
> > > > > > > > Following getdents calls traverse the readdir cache list and call
> > > > > > > > ovl_cache_update_ino() for entries with zero p->ino to lookup the entry
> > > > > > > > in the overlay and return d_ino that is consistent with st_ino.
> > > > > > > >
> > > > > > > > If the upper file was unlinked between the first getdents call and the
> > > > > > > > getdents call that lists the file entry, ovl_cache_update_ino() will not
> > > > > > > > find the entry and fall back to setting d_ino to the upper real st_ino,
> > > > > > > > which is inconsistent with how this object was presented to users.
> > > > > > > >
> > > > > > > > Instead of listing a stale entry with inconsistent d_ino, simply skip
> > > > > > > > the stale entry, which is better for users.
> > > > > > > >
> > > > > > >
> > > > > > > Miklos,
> > > > > > >
> > > > > > > I forgot to follow up on this patch.
> > > > > > > Upstream xfstest overlay/077 is failing without this patch.
> > > > > >
> > > > > > Can't reproduce (on ext4/xfs and "-oxino=on").
> > > > > >
> > > > > > Is there some trick?
> > > > >
> > > > > Not sure. overlay/077 fails for me on v5.14.0-rc2 on ext4/xfs.
> > > > >
> > > > >      QA output created by 077
> > > > >     +entry m100 has inconsistent d_ino (234 != 232)
> > > > >     +entry f100 has inconsistent d_ino (335 != 16777542)
> > > > >      Silence is golden
> > > > >
> > > > > Maybe you need to build src/t_dir_offset2?
> > > >
> > > > root@kvm:/opt/xfstests-dev# git log -1 --pretty=%h
> > > > 10f6b231
> > > > root@kvm:/opt/xfstests-dev# cat local.config
> > > > export TEST_DEV=/dev/vdb1
> > > > export TEST_DIR=/test
> > > > export SCRATCH_DEV=/dev/vdb2
> > > > export SCRATCH_MNT=/scratch
> > > > export FSTYP=ext4
> > > > export OVERLAY_MOUNT_OPTIONS="-o xino=on"
> > > > root@kvm:/opt/xfstests-dev# make src/t_dir_offset2
> > > > make: 'src/t_dir_offset2' is up to date.
> > > > root@kvm:/opt/xfstests-dev# ./check -overlay overlay/077
> > > > FSTYP         -- overlay
> > > > PLATFORM      -- Linux/x86_64 kvm 5.14.0-rc2 #276 SMP Tue Jul 20
> > > > 05:54:44 CEST 2021
> > > > MKFS_OPTIONS  -- /scratch
> > > > MOUNT_OPTIONS -- -o xino=on /scratch /scratch/ovl-mnt
> > > >
> > > > overlay/077 1s ...  1s
> > > > Ran: overlay/077
> > > > Passed all 1 tests
> > > >
> > > > root@kvm:/opt/xfstests-dev# cat results/overlay/077.full
> > > >
> > > > Create file in pure upper dir:
> > > > getdents at offset 0 returned 192 bytes
> > > > created entry p0
> > > > entry p0 found as expected
> > > >
> > > > Remove file in pure upper dir:
> > > > getdents at offset 0 returned 192 bytes
> > > > unlinked entry p100
> > > > entry p100 not found as expected
> > > >
> > > > Create file in impure upper dir:
> > > > getdents at offset 0 returned 192 bytes
> > > > created entry o0
> > > > entry o0 found as expected
> > > >
> > > > Remove file in impure upper dir:
> > > > getdents at offset 0 returned 192 bytes
> > > > unlinked entry o100
> > > > entry o100 not found as expected
> > > >
> > > > Create file in merge dir:
> > > > getdents at offset 0 returned 192 bytes
> > > > created entry m0
> > > > entry m0 found as expected
> > > >
> > > > Remove file in merge dir:
> > > > getdents at offset 0 returned 192 bytes
> > > > unlinked entry m100
> > > > entry m100 not found as expected
> > > >
> > > > Create file in former merge dir:
> > > > getdents at offset 0 returned 192 bytes
> > > > created entry f0
> > > > entry f0 found as expected
> > > >
> > > > Remove file in former merge dir:
> > > > getdents at offset 0 returned 192 bytes
> > > > unlinked entry f100
> > > > entry f100 not found as expected
> > > >
> > > > Ideas for further debugging why this test isn't failing for v4.12-rc2?
> > >
> >
> > It's not you, it's me ;-)
> >
> > The failure was lost during cleanup of t_dir_offset2 patches
> > for submission and it is I who was running an older version
> > of t_dir_offset2. Let me figure this out and get back to you
> > with a working test.
> >
>
> How about you try again with a version of the test that actually has
> the check and the error print that I reported.... ;-)
>

P.S.1:
xino=on is futile for this test as it uses all layers on same fs

P.S.2:
The attached patch to t_dir_offset2 only reproduces the first
inconsistency I reported:
entry m100 has inconsistent d_ino (234 != 232)

The second inconsistency requires another small patch to overlay/077
(attached). I will post both those patches once the kernel fix is in
overlayfs-next.

Thanks,
Amir.

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From e64a7b0c1ce697745c0bdb3ef8f43f0764510ef8 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Tue, 20 Jul 2021 19:11:03 +0300
Subject: [PATCH] overlay/077: test inconsistent d_ino in former merge dir

For testing of inconsistent d_ino/st_ino we need to unlink an entry
whose st_ino is not that of the upper inode.

In the former merge dir setup we unlink all the files in the lower
dir after copyup, so they all use st_ino of the upper inode.

Let the unlinked file f100 reside in a lower path that is not being
unlinked so it will have the st_ino of the lower inode.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 tests/overlay/077 | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tests/overlay/077 b/tests/overlay/077
index 58c0f3b5..04cb3881 100755
--- a/tests/overlay/077
+++ b/tests/overlay/077
@@ -61,8 +61,8 @@ mkdir -p $lowerdir/merge $lowerdir/former $upperdir/pure $upperdir/impure
 create_files $lowerdir/merge m
 # Files to be moved into impure upper dir
 create_files $lowerdir o
-# File to be copied up to make former merge dir impure
-touch $lowerdir/former/f100
+# File to be moved into former merge dir to make it impure
+touch $lowerdir/f100
 
 _scratch_mount
 
@@ -72,6 +72,7 @@ create_files $SCRATCH_MNT/former f
 touch $SCRATCH_MNT/merge/m100
 # Move copied up files so readdir will need to lookup origin d_ino
 mv $SCRATCH_MNT/o* $SCRATCH_MNT/impure/
+mv $SCRATCH_MNT/f100 $SCRATCH_MNT/former/
 
 # Remove the lower directory and mount overlay again to create
 # a "former merge dir"
-- 
2.32.0