From: Vivek Goyal <vgoyal@redhat.com>
To: Amir Goldstein <amir73il@gmail.com>
Cc: overlayfs <linux-unionfs@vger.kernel.org>,
Miklos Szeredi <miklos@szeredi.hu>,
"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH 5/9] ovl: Set xattr OVL_XATTR_METACOPY on upper file
Date: Wed, 11 Oct 2017 16:16:30 -0400 [thread overview]
Message-ID: <20171011201630.GE8086@redhat.com> (raw)
In-Reply-To: <CAOQ4uxgNg3SO=xyvh_oAH-ExQGQCWXMGKygdAhmGeDdanyo=vA@mail.gmail.com>
On Tue, Oct 10, 2017 at 08:03:05PM +0300, Amir Goldstein wrote:
[..]
> > @@ -511,6 +564,10 @@ static int ovl_copy_up_locked(struct ovl_copy_up_ctx *c)
> > goto out_cleanup;
> >
> > ovl_inode_update(d_inode(c->dentry), newdentry);
> > + if (c->metadata_only) {
> > + smp_wmb();
>
> This wmb does not address the only problem imo.
> The problem is you must not allow inode to appear to have
> An upper dentry before you made sure metacopy flag is visible.
> So first you need to set metacopy flag before updating upper.
> Then you also need to test them is correct order with rmb.
Ok, so conceptually it makse sense to me that OVL_METACOPY flag should
be set before upper dentry is made visible.
So ovl_set_flag(OVL_METACOPY) should move before ovl_inode_update().
ovl_inode_update() already has a smp_wmb(). So write side is probably
fine.
But read side, ovl_upperdentry_dereference() only has data dependency
barrier and not smp_rmb(). (lockless_dereference(oi->__upperdentry)). I
am not sure if that's sufficient for ovl_inode->flags read or not. May
be we need to replace data dependency barrier with smp_rmb() in in
ovl_upperdentry_dereference()?
Even if we do this, I think we need barriers around setting/resetting
of OVL_METACOPY for the reset case. I will explain this in other patch.
Vivek
next prev parent reply other threads:[~2017-10-11 20:16 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-10 15:32 [RFC PATCH 0/9][V3] overlayfs: Delayed copy up of data Vivek Goyal
2017-10-10 15:32 ` [PATCH 1/9] ovl: ovl_check_setxattr() get rid of redundant -EOPNOTSUPP check Vivek Goyal
2017-10-10 15:32 ` [PATCH 2/9] ovl: During copy up, first copy up metadata and then data Vivek Goyal
2017-10-10 15:32 ` [PATCH 3/9] ovl: Provide a mount option metacopy=on/off for metadata copyup Vivek Goyal
2017-10-11 1:36 ` Amir Goldstein
2017-10-11 13:57 ` Vivek Goyal
2017-10-11 16:29 ` Amir Goldstein
2017-10-11 16:53 ` Vivek Goyal
2017-10-11 17:36 ` Amir Goldstein
2017-10-11 18:34 ` Vivek Goyal
2017-10-11 20:29 ` Amir Goldstein
2017-10-12 13:23 ` Vivek Goyal
2017-10-12 13:39 ` Amir Goldstein
2017-10-10 15:32 ` [PATCH 4/9] ovl: Copy up only metadata during copy up where it makes sense Vivek Goyal
2017-10-10 15:32 ` [PATCH 5/9] ovl: Set xattr OVL_XATTR_METACOPY on upper file Vivek Goyal
2017-10-10 17:03 ` Amir Goldstein
2017-10-11 20:16 ` Vivek Goyal [this message]
2017-10-11 20:44 ` Amir Goldstein
2017-10-10 15:32 ` [PATCH 6/9] ovl: Fix ovl_getattr() to get number of blocks from lower Vivek Goyal
2017-10-10 15:32 ` [PATCH 7/9] ovl: Introduce read/write barriers around metacopy flag update Vivek Goyal
2017-10-10 17:12 ` Amir Goldstein
2017-10-11 20:27 ` Vivek Goyal
2017-10-11 21:08 ` Amir Goldstein
2017-10-13 18:27 ` Vivek Goyal
2017-10-14 6:05 ` Amir Goldstein
2017-10-14 7:00 ` Amir Goldstein
2017-10-16 13:24 ` Vivek Goyal
2017-10-16 13:24 ` Vivek Goyal
2017-10-16 13:31 ` Amir Goldstein
2017-10-10 15:32 ` [PATCH 8/9] ovl: Set OVL_METACOPY flag during ovl_lookup() Vivek Goyal
2017-10-10 15:32 ` [PATCH 9/9] ovl: Return lower dentry if only metadata copy up took place Vivek Goyal
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