Re: [PATCH v2] xfs: handle register_shrinker error

Darrick J. Wong
2017-11-27T17:45:26Z

On Fri, Nov 24, 2017 at 08:39:57AM +0100, Michal Hocko wrote:
> On Fri 24-11-17 09:00:46, Dave Chinner wrote:
> > On Thu, Nov 23, 2017 at 05:11:37PM +0100, Michal Hocko wrote:
> > > On Fri 24-11-17 01:01:10, Tetsuo Handa wrote:
> > > > Michal Hocko wrote:
> > > > > On Thu 23-11-17 05:26:33, Christoph Hellwig wrote:
> > > > > > Looks good,
> > > > > >
> > > > > > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > > > >
> > > > > Thanks!
> > > > >
> > > > > > I can take a stab at the quota one.
> > > > >
> > > > > That would be really great!
> > > > >
> > > > Again, it does not look good. Since kmem_free() does only kvfree(),
> > > > nothing will release memory allocated by list_lru_init().
> > >
> > > Hmm, you are right. I have (blindly) followed the current code flow
> > > which is wrong as well. The following should do the trick. Should I
> > > split that into two patches?
> >
> > One is fine by me - if we're need to backport one fix, then we need
> > to backport both :/
>
> OK
>
> > > ---
> > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> > > index dd0e18af990c..4c6e86d861fd 100644
> > > --- a/fs/xfs/xfs_buf.c
> > > +++ b/fs/xfs/xfs_buf.c
> > > @@ -1815,25 +1815,27 @@ xfs_alloc_buftarg(
> > > btp->bt_daxdev = dax_dev;
> > >
> > > if (xfs_setsize_buftarg_early(btp, bdev))
> > > - goto error;
> > > + goto error_free;
> > >
> > > if (list_lru_init(&btp->bt_lru))
> > > - goto error;
> > > + goto error_free;
> > >
> > > if (percpu_counter_init(&btp->bt_io_count, 0, GFP_KERNEL))
> > > - goto error;
> > > + goto error_lru;
> > >
> > > btp->bt_shrinker.count_objects = xfs_buftarg_shrink_count;
> > > btp->bt_shrinker.scan_objects = xfs_buftarg_shrink_scan;
> > > btp->bt_shrinker.seeks = DEFAULT_SEEKS;
> > > btp->bt_shrinker.flags = SHRINKER_NUMA_AWARE;
> > > - if (register_shrinker(&btp->bt_shrinker)) {
> > > - percpu_counter_destroy(&btp->bt_io_count);
> > > - goto error;
> > > - }
> > > + if (register_shrinker(&btp->bt_shrinker))
> > > + goto error_pcpu;
> > > return btp;
> > >
> > > -error:
> > > +error_pcpu:
> > > + percpu_counter_destroy(&btp->bt_io_count);
> > > +error_lru:
> > > + list_lru_destroy(&btp->bt_lru);
> > > +error_free:
> > > kmem_free(btp);
> > > return NULL;
> >
> > That should do the trick.
> >
> > Acked-by: Dave Chinner <dchinner@redhat.com>
>
> Thanks. Updated patch below
> ---
> From 1009db61988c48c9a9e327a9d076945b29b02eee Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.com>
> Date: Thu, 23 Nov 2017 17:13:40 +0100
> Subject: [PATCH] xfs: fortify xfs_alloc_buftarg error handling
>
> percpu_counter_init failure path doesn't clean up &btp->bt_lru list.
> Call list_lru_destroy in that error path. Similarly register_shrinker
> error path is not handled.
>
> While it is unlikely to trigger these error path, it is not impossible
> especially the later might fail with large NUMAs. Let's handle the
> failure to make the code more robust.
>
> Acked-by: Dave Chinner <dchinner@redhat.com>
> Noticed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> fs/xfs/xfs_buf.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 4db6e8d780f6..4c6e86d861fd 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1815,22 +1815,27 @@ xfs_alloc_buftarg(
> btp->bt_daxdev = dax_dev;
>
> if (xfs_setsize_buftarg_early(btp, bdev))
> - goto error;
> + goto error_free;
>
> if (list_lru_init(&btp->bt_lru))
> - goto error;
> + goto error_free;
>
> if (percpu_counter_init(&btp->bt_io_count, 0, GFP_KERNEL))
> - goto error;
> + goto error_lru;
>
> btp->bt_shrinker.count_objects = xfs_buftarg_shrink_count;
> btp->bt_shrinker.scan_objects = xfs_buftarg_shrink_scan;
> btp->bt_shrinker.seeks = DEFAULT_SEEKS;
> btp->bt_shrinker.flags = SHRINKER_NUMA_AWARE;
> - register_shrinker(&btp->bt_shrinker);
> + if (register_shrinker(&btp->bt_shrinker))
> + goto error_pcpu;
> return btp;
>
> -error:
> +error_pcpu:
> + percpu_counter_destroy(&btp->bt_io_count);
> +error_lru:
> + list_lru_destroy(&btp->bt_lru);
> +error_free:
> kmem_free(btp);
> return NULL;

This part looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

> }
> --
> 2.15.0
>
> --
> Michal Hocko
> SUSE Labs
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