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Reply-To: fdmanana@gmail.com
From:   Filipe Manana <fdmanana@gmail.com>
Date:   Mon, 20 Apr 2020 18:35:56 +0100
Message-ID: <CAL3q7H4Yr2cdEgLWVAR2N_hPYEsra8yLA89meUMcvxH1VjtA6A@mail.gmail.com>
Subject: Re: [PATCH] btrfs: Fix refcnt leak in btrfs_recover_relocation
To:     Xiyu Yang <xiyuyang19@fudan.edu.cn>
Cc:     Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>, Jeff Mahoney <jeffm@suse.com>,
        linux-btrfs <linux-btrfs@vger.kernel.org>,
        linux-kernel@vger.kernel.org, yuanxzhang@fudan.edu.cn,
        kjlu@umn.edu, Xin Tan <tanxin.ctf@gmail.com>
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On Mon, Apr 20, 2020 at 6:34 PM Filipe Manana <fdmanana@gmail.com> wrote:
>
> On Mon, Apr 20, 2020 at 6:50 AM Xiyu Yang <xiyuyang19@fudan.edu.cn> wrote=
:
> >
> > btrfs_recover_relocation() invokes btrfs_join_transaction(), which join=
s
> > a btrfs_trans_handle object into transactions and returns a reference o=
f
> > it with increased refcount to "trans".
> >
> > When btrfs_recover_relocation() returns, "trans" becomes invalid, so th=
e
> > refcount should be decreased to keep refcount balanced.
> >
> > The reference counting issue happens in one exception handling path of
> > btrfs_recover_relocation(). When read_fs_root() failed, the refcnt
> > increased by btrfs_join_transaction() is not decreased, causing a refcn=
t
> > leak.
> >
> > Fix this issue by calling btrfs_end_transaction() on this error path
> > when read_fs_root() failed.
> >
> > Fixes: 79787eaab461 ("btrfs: replace many BUG_ONs with proper error
> > handling")
> > Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
> > Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
>
> Reviewed-by: Filipe Manana <fdmanana@suse.com>
>
> Looks good, thanks.

Btw, the subject could be more clear.
Instead of

"btrfs: Fix refcnt leak in btrfs_recover_relocation"

something like

"btrfs: fix transaction leak in ..."

David can probably fixup that when he picks the patch.

Thanks.

>
> > ---
> >  fs/btrfs/relocation.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> > index 995d4b8b1cfd..46a451594c7a 100644
> > --- a/fs/btrfs/relocation.c
> > +++ b/fs/btrfs/relocation.c
> > @@ -4606,6 +4606,7 @@ int btrfs_recover_relocation(struct btrfs_root *r=
oot)
> >                 if (IS_ERR(fs_root)) {
> >                         err =3D PTR_ERR(fs_root);
> >                         list_add_tail(&reloc_root->root_list, &reloc_ro=
ots);
> > +                       btrfs_end_transaction(trans);
> >                         goto out_free;
> >                 }
> >
> > --
> > 2.7.4
> >
>
>
> --
> Filipe David Manana,
>
> =E2=80=9CWhether you think you can, or you think you can't =E2=80=94 you'=
re right.=E2=80=9D


--=20
Filipe David Manana,

=E2=80=9CWhether you think you can, or you think you can't =E2=80=94 you're=
 right.=E2=80=9D