linux-kernel - Re: [PATCH -next] fs/btrfs: Fix unlocking in btrfs_ref_tree

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Message-ID: <CAKq8=3L7u05wneTt=DRPNU6dCrg=OMN-Zcp9XgTcd3MWbjPKUg@mail.gmail.com>
Date:   Fri, 15 May 2020 18:44:44 +0800
From:   Bo YU <tsu.yubo@...il.com>
To:     Johannes Thumshirn <Johannes.Thumshirn@....com>
Cc:     "clm@...com" <clm@...com>,
        "josef@...icpanda.com" <josef@...icpanda.com>,
        "sterba@...e.com" <sterba@...e.com>,
        "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] fs/btrfs: Fix unlocking in btrfs_ref_tree_mod

On Fri, May 15, 2020 at 5:36 PM Johannes Thumshirn
<Johannes.Thumshirn@....com> wrote:
>
> On 15/05/2020 11:24, Bo YU wrote:
> > Hi,
> > On Fri, May 15, 2020 at 5:03 PM Johannes Thumshirn
> > <Johannes.Thumshirn@....com> wrote:
> >>
> >> On 15/05/2020 04:17, Bo YU wrote:
> >>> It adds spin_lock() in add_block_entry() but out path does not unlock
> >>> it.
> >>
> >> Which call path doesn't unlock it? There is an out_unlock label with a
> >> spin_unlock() right above your insert. So either coverity messed something
> >> up or the call path that needs the unlock has to jump to out_unlock instead
> >> of out.
> > This is out label without unlocking it. It will be offered spin_lock
> > in add_block_entry()
> > for be. But here I was worried about that unlock it in if() whether it
> > is right or not.
> >
>
> No add_block_entry() returns with the ref_verify_lock held on success only:
> static struct block_entry *add_block_entry(struct btrfs_fs_info *fs_info,
>                                            u64 bytenr, u64 len,
>                                            u64 root_objectid)
> {
>         struct block_entry *be = NULL, *exist;
>         struct root_entry *re = NULL;
>
>         re = kzalloc(sizeof(struct root_entry), GFP_KERNEL);
>         be = kzalloc(sizeof(struct block_entry), GFP_KERNEL);
>         if (!be || !re) {
>                 kfree(re);
>                 kfree(be);
>                 return ERR_PTR(-ENOMEM);
>         }
>         be->bytenr = bytenr;
>         be->len = len;
>
>         re->root_objectid = root_objectid;
>         re->num_refs = 0;
>
>         spin_lock(&fs_info->ref_verify_lock);
> [...]
>
>
> While the code caller checks for an error:
>
> if (action == BTRFS_ADD_DELAYED_EXTENT) {
>                 /*
>                  * For subvol_create we'll just pass in whatever the parent root
>                  * is and the new root objectid, so let's not treat the passed
>                  * in root as if it really has a ref for this bytenr.
>                  */
>                 be = add_block_entry(fs_info, bytenr, num_bytes, ref_root);
>                 if (IS_ERR(be)) {
>                         kfree(ref);
>                         kfree(ra);
>                         ret = PTR_ERR(be);
>                         goto out;
>                 }
>
> So if add_block_entry returns -ENOMEM it didn't take the lock and thus no unlock
> is needed.
Ok,  I got it. Please drop it.
Thank you!
>
> Or did I miss something?