Re: [RFC][PATCH] xfs: preserve i_rdev when recycling a reclaimable inode

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Jan 26, 2018 at 08:51:01AM +0200, Amir Goldstein wrote:
> On Thu, Jan 25, 2018 at 11:30 PM, Darrick J. Wong
> <darrick.wong@oracle.com> wrote:
> > On Thu, Jan 25, 2018 at 11:21:38PM +0200, Amir Goldstein wrote:
> >> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> >> ---
> >>
> >> Darrick,
> >>
> >> This patch fixes a problem I am hitting consistenty with xfstest
> >> overlay/017 with certain overlay mount options (index=on,nfs_export=off).
> >>
> >> I see that overlayfs looks up in underlying xfs and gets a chardev
> >> or blockdev inode with non initialized i_rdev (these are not whiteout
> >> inodes).
> >>
> >> It takes a certain timing which happens in this test that does lookup
> >> immediately after drop caches. The test causes a permanent error in
> >> inode cache of xfs that is only fixed after another drop caches or
> >> cycle mount.
> >>
> >> So I am certain there is a problem and that this patch fixes the
> >> problem, I'm just not sure this is the right fix and if it is, which
> >> is the commit that it "Fixes".
> >
> > We're basically reinitializing a VFS inode that was on its way to being
> > reclaimed, which means that we don't xfs_iread.  We still have to
> > reinitialize the vfs inode state (because we'd already torn that down),
> > so we have to preserve all the vfs inode state that the xfs inode stores
> > in the vfs inode.
> >
> > Oh, right, hch moved if_rdev to i_rdev in 66f364649d870 ("xfs: remove
> > if_rdev") but forgot the xfs_reinit_inode usage.  so that would be the
> > commit that this fixes.  Doh.
> >
> 
> Then this is a v4.15 regression fix and worth a last minute pull request IMO.
> Devices may become unavailable under memory pressure... weird things can happen.

It probably ought to have a proper changelog & Fixes: tag then.

--D

> 
> >
> >>
> >> Thanks,
> >> Amir.
> >>
> >>  fs/xfs/xfs_icache.c | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> >> index 3861d61fb265..3ce946063ffe 100644
> >> --- a/fs/xfs/xfs_icache.c
> >> +++ b/fs/xfs/xfs_icache.c
> >> @@ -295,6 +295,7 @@ xfs_reinit_inode(
> >>       uint32_t        generation = inode->i_generation;
> >>       uint64_t        version = inode->i_version;
> >>       umode_t         mode = inode->i_mode;
> >> +     dev_t           dev = inode->i_rdev;
> >>
> >>       error = inode_init_always(mp->m_super, inode);
> >>
> >> @@ -302,6 +303,7 @@ xfs_reinit_inode(
> >>       inode->i_generation = generation;
> >>       inode->i_version = version;
> >>       inode->i_mode = mode;
> >> +     inode->i_rdev = dev;
> >>       return error;
> >>  }
> >>
> >> --
> >> 2.7.4
> >>
> >> --
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