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From: Amir Goldstein <amir73il@gmail.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Eryu Guan <guaneryu@gmail.com>,
	overlayfs <linux-unionfs@vger.kernel.org>,
	fstests <fstests@vger.kernel.org>
Subject: Re: [PATCH v2 0/5] Test overlayfs readdir cache
Date: Mon, 26 Apr 2021 18:22:28 +0300	[thread overview]
Message-ID: <CAOQ4uxgR_cLnC_vdU5=seP3fwqVkuZM_-WfD6maFTMbMYq=a9w@mail.gmail.com> (raw)
In-Reply-To: <CAJfpegvf=6FPgSBfz73Lu+7DV2T8A+E4CzzsNjfqSbmJccY4VA@mail.gmail.com>

[-- Attachment #1: Type: text/plain, Size: 1119 bytes --]

On Mon, Apr 26, 2021 at 4:13 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
> On Mon, Apr 26, 2021 at 12:15 PM Amir Goldstein <amir73il@gmail.com> wrote:
> >
> > On Mon, Apr 26, 2021 at 1:07 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
> > > The other case you found it that in case of a stale direntry the i_ino
> > > update will be skipped and so it will return an inconsistent result,
> > > right?
> >
> > Right. It returns a stale entry with the old real ino.
> > Not sure if that is an "inconsistent" result.
> > inconsistent w.r.t what?
> It's inconsistent with previous (before the entry got deleted)
> st_ino/i_ino.  This should actually be testable.

Right. it is testable:

     QA output created by 077
    +entry m100 has inconsistent d_ino (266 != 264)
    +entry f100 has inconsistent d_ino (367 != 16777542)
     Silence is golden

These prints are from the iteration on the first fd.
The first fd lists the stale entry with inconsistent d_ino.
The second fd does not list the stale entry (with bugfix in linux-next).
Will add it to the test in V3.

Attached patch fixes this problem.


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From 304e1599cc112fae388d0c0b2aaabdf385032226 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Mon, 26 Apr 2021 18:07:09 +0300
Subject: [PATCH] ovl: skip stale entries in merge dir cache iteration

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.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
 fs/overlayfs/readdir.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index cc1e80257064..10b7780e4bdc 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -481,6 +481,8 @@ static int ovl_cache_update_ino(struct path *path, struct ovl_cache_entry *p)
 	this = lookup_one_len(p->name, dir, p->len);
 	if (IS_ERR_OR_NULL(this) || !this->d_inode) {
+		/* Mark a stale entry */
+		p->is_whiteout = true;
 		if (IS_ERR(this)) {
 			err = PTR_ERR(this);
 			this = NULL;
@@ -776,6 +778,9 @@ static int ovl_iterate(struct file *file, struct dir_context *ctx)
 				if (err)
 					goto out;
+		}
+		/* ovl_cache_update_ino() sets is_whiteout on stale entry */
+		if (!p->is_whiteout) {
 			if (!dir_emit(ctx, p->name, p->len, p->ino, p->type))

      reply	other threads:[~2021-04-26 15:22 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-25  7:14 [PATCH v2 0/5] Test overlayfs readdir cache Amir Goldstein
2021-04-25  7:14 ` [PATCH v2 1/5] src/t_dir_offset2: Add an option to limit of buffer size Amir Goldstein
2021-04-25  7:14 ` [PATCH v2 2/5] src/t_dir_offset2: Add an option to find file by name Amir Goldstein
2021-04-25  7:14 ` [PATCH v2 3/5] src/t_dir_offset2: Add option to create or unlink file Amir Goldstein
2021-04-25  7:14 ` [PATCH v2 4/5] generic: Test readdir of modified directrory Amir Goldstein
2021-04-25  7:14 ` [PATCH v2 5/5] overlay: Test invalidate of readdir cache Amir Goldstein
2021-04-26 10:07 ` [PATCH v2 0/5] Test overlayfs " Miklos Szeredi
2021-04-26 10:15   ` Amir Goldstein
2021-04-26 13:12     ` Miklos Szeredi
2021-04-26 15:22       ` Amir Goldstein [this message]

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