Re: [PATCH] ceph: fix memory leak in ceph_cleanup_snapid_map

[Luis Henriques <lhenriques@suse.com>]

On Thu, Mar 19, 2020 at 10:41:13AM -0400, Jeff Layton wrote:
> On Thu, 2020-03-19 at 11:43 +0000, Luis Henriques wrote:
> > kmemleak reports the following memory leak:
> > 
> > unreferenced object 0xffff88821feac8a0 (size 96):
> >   comm "kworker/1:0", pid 17, jiffies 4294896362 (age 20.512s)
> >   hex dump (first 32 bytes):
> >     a0 c8 ea 1f 82 88 ff ff 00 c9 ea 1f 82 88 ff ff  ................
> >     00 00 00 00 00 00 00 00 00 01 00 00 00 00 ad de  ................
> >   backtrace:
> >     [<00000000b3ea77fb>] ceph_get_snapid_map+0x75/0x2a0
> >     [<00000000d4060942>] fill_inode+0xb26/0x1010
> >     [<0000000049da6206>] ceph_readdir_prepopulate+0x389/0xc40
> >     [<00000000e2fe2549>] dispatch+0x11ab/0x1521
> >     [<000000007700b894>] ceph_con_workfn+0xf3d/0x3240
> >     [<0000000039138a41>] process_one_work+0x24d/0x590
> >     [<00000000eb751f34>] worker_thread+0x4a/0x3d0
> >     [<000000007e8f0d42>] kthread+0xfb/0x130
> >     [<00000000d49bd1fa>] ret_from_fork+0x3a/0x50
> > 
> > A kfree was missing in commit 75c9627efb72 ("ceph: map snapid to anonymous
> > bdev ID"), while looping the 'to_free' list of ceph_snapid_map objects.
> > 
> > Fixes: 75c9627efb72 ("ceph: map snapid to anonymous bdev ID")
> > Signed-off-by: Luis Henriques <lhenriques@suse.com>
> > ---
> > Hi!
> > 
> > A bit of mailing-list archaeology shows that v1 of this patch actually
> > included this kfree [1], and was lost on v2 [2].
> > 
> > [1] https://patchwork.kernel.org/patch/10114319/
> > [2] https://patchwork.kernel.org/patch/10749907/
> > 
> > Cheers,
> > --
> > Luis
> > 
> > fs/ceph/snap.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
> > index ccfcc66aaf44..923be9399b21 100644
> > --- a/fs/ceph/snap.c
> > +++ b/fs/ceph/snap.c
> > @@ -1155,5 +1155,6 @@ void ceph_cleanup_snapid_map(struct ceph_mds_client *mdsc)
> >  			pr_err("snapid map %llx -> %x still in use\n",
> >  			       sm->snap, sm->dev);
> >  		}
> > +		kfree(sm);
> >  	}
> >  }
> 
> Good catch. This looks correct to me.
> 
> Hmmm...we'll leak one of these for every snapid we encounter. Any
> objection to marking this for stable?

No, please do.  I assumed it would be a stable candidate already by having
the 'Fixes: <sha1>' but maybe it's better to explicitly tag it.

Cheers,
--
Luis