Date:   Sun, 25 Mar 2018 23:48:19 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Sasha Levin <Alexander.Levin@...rosoft.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Christoph Hellwig <hch@....de>,
        xfs <linux-xfs@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Julia Lawall <julia.lawall@...6.fr>,
        Josh Triplett <josh@...htriplett.org>,
        Takashi Iwai <tiwai@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] xfs: always free inline data before resetting inode fork
 during ifree

On Mon, Mar 26, 2018 at 04:54:59AM +0000, Sasha Levin wrote:
> On Sat, Mar 24, 2018 at 10:21:59AM -0700, Darrick J. Wong wrote:
> >On Sat, Mar 24, 2018 at 10:06:38AM +0100, Greg Kroah-Hartman wrote:
> >> On Fri, Mar 23, 2018 at 06:23:02PM +0000, Luis R. Rodriguez wrote:
> >> > On Fri, Mar 23, 2018 at 10:26:20AM -0700, Darrick J. Wong wrote:
> >> > > On Fri, Mar 23, 2018 at 05:08:13PM +0000, Luis R. Rodriguez wrote:
> >> > > > On Thu, Mar 22, 2018 at 08:41:45PM -0700, Darrick J. Wong wrote:
> >> > > > > On Fri, Mar 23, 2018 at 01:30:37AM +0000, Luis R. Rodriguez wrote:
> >> > > > > > On Wed, Nov 22, 2017 at 10:01:37PM -0800, Darrick J. Wong wrote:
> >> > > > > > > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> >> > > > > > > index 61d1cb7..8012741 100644
> >> > > > > > > --- a/fs/xfs/xfs_inode.c
> >> > > > > > > +++ b/fs/xfs/xfs_inode.c
> >> > > > > > > @@ -2401,6 +2401,24 @@ xfs_ifree_cluster(
> >> > > > > > >  }
> >> > > > > > >
> >> > > > > > >  /*
> >> > > > > > > + * Free any local-format buffers sitting around before we reset to
> >> > > > > > > + * extents format.
> >> > > > > > > + */
> >> > > > > > > +static inline void
> >> > > > > > > +xfs_ifree_local_data(
> >> > > > > > > +	struct xfs_inode	*ip,
> >> > > > > > > +	int			whichfork)
> >> > > > > > > +{
> >> > > > > > > +	struct xfs_ifork	*ifp;
> >> > > > > > > +
> >> > > > > > > +	if (XFS_IFORK_FORMAT(ip, whichfork) != XFS_DINODE_FMT_LOCAL)
> >> > > > > > > +		return;
> >> > > > > >
> >> > > > > > I'm new to all this so this was a bit hard to follow. I'm confused with how
> >> > > > > > commit 43518812d2 ("xfs: remove support for inlining data/extents into the
> >> > > > > > inode fork") exacerbated the leak, isn't that commit about
> >> > > > > > XFS_DINODE_FMT_EXTENTS?
> >> > > > >
> >> > > > > Not specifically _EXTENTS, merely any fork (EXTENTS or LOCAL) whose
> >> > > > > incore data was small enough to fit in if_inline_ata.
> >> > > >
> >> > > > Got it, I thought those were XFS_DINODE_FMT_EXTENTS by definition.
> >> > > >
> >> > > > > > Did we have cases where the format was XFS_DINODE_FMT_LOCAL and yet
> >> > > > > > ifp->if_u1.if_data == ifp->if_u2.if_inline_data ?
> >> > > > >
> >> > > > > An empty directory is 6 bytes, which is what you get with a fresh mkdir
> >> > > > > or after deleting everything in the directory.  Prior to the 43518812d2
> >> > > > > patch we could get away with not even checking if we had to free if_data
> >> > > > > when deleting a directory because it fit within if_inline_data.
> >> > > >
> >> > > > Ah got it. So your fix *is* also applicable even prior to commit 43518812d2.
> >> > >
> >> > > You'd have to modify the patch so that it doesn't try to kmem_free
> >> > > if_data if if_data == if_inline_data but otherwise (in theory) I think
> >> > > that the concept applies to pre-4.15 kernels.
> >> > >
> >> > > (YMMV, please do run this through QA/kmemleak just in case I'm wrong, etc...)
> >> >
> >> > Well... so we need a resolution and better get testing this already given that
> >> > *I believe* the new auto-selection algorithm used to cherry pick patches onto
> >> > stable for linux-4.14.y (covered on a paper [0] and when used, stable patches
> >> > are prefixed with AUTOSEL, a recent discussion covered this in November 2017
> >> > [1]) recommended to merge your commit 98c4f78dcdd8 ("xfs: always free inline
> >> > data before resetting inode fork during ifree") as stable commit 1eccdbd4836a41
> >> > on v4.14.17 *without* merging commit 43518812d2 ("xfs: remove support for
> >> > inlining data/extents into the inode fork").
> >> >
> >> > Sasha, Greg,
> >> >
> >> > Can you confirm if the algorithm was used in this case?
> >>
> >> No idea.
> >>
> >> I think xfs should just be added to the "blacklist" so that it is not
> >> even looked at for these types of auto-selected patches.  Much like the
> >> i915 driver currently is handled (it too is ignored for these patches
> >> due to objections from the maintainers of it.)
> >
> >Just out of curiosity, how does this autoselection mechanism work today?
> >If it's smart enough to cherry pick patches, apply them to a kernel,
> >build the kernel and run xfstests, and propose the patches if nothing
> >weird happened, then I'd be interested in looking further.  I've nothing
> >against algorithmic selection per se, but I'd want to know more about
> >the data sets and parameters that feed the algorithm.
> 
> It won't go beyond build testing.

No further regression testing ==> please blacklist XFS.

We will continue our current practices w.r.t. stable.

--D

> >I did receive the AUTOSEL tagged patches a few days ago, but I couldn't
> >figure out what automated regression testing, if any, had been done; or
> >whether the patch submission was asking if we wanted it put into 4.14
> >or if it was a declaration that they were on their way in.  Excuse me
> 
> There would be (at least) 3 different mails involved in this process:
> 
>  1. You'd get a mail from me, proposing this patch for stable. We give
>  at least 1 week (but usually closer to 2) to comment on whether this
>  patch should or should not go in stable.
> 
>  2. If no objections were received, Greg would add it to his queue and
>  you'd get another mail about that.
> 
>  3. A few more days later, Greg would release that stable tree and you'd
>  get another mail.
> 
> >for being behind the times, but I'd gotten accustomed xfs patches only
> >ending up in the stable kernels because we'd deliberately put them
> >there. :)
> >
> >If blacklisting xfs is more convenient then I'm happy to continue things
> >as they were.
> 
> No problem with blacklisting subsystems if maintainers prefer it that
> way, but the i915 case was slightly different as their development
> process was very quirky and testing was complex, so they asked to just
> keep doing their own selection for stable.
> 
> However, looking at stable history, it seems that no patch from fs/xfs/
> was proposed for stable for about half a year now, which is something
> that the autoselection project is trying to help with.
> 
> A different flow I'm working on for this is to send an email as a reply
> to the original patch submission to lkml if the patch is selected by the
> network, including details about which trees it was applied to and build
> results. I think it might work better for subsystems such as xfs.
> 
> 
> --
> Thanks,
> Sasha--
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