linux-kernel - Re: [PATCH] Btrfs: remove BUG_ON from get_restripe

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Message-ID: <CAArOQ2XoGCgc7nwcxwfzLEzA2Scj3GMnOOmzyT+NREi0AMWQrQ@mail.gmail.com>
Date:	Wed, 4 Apr 2012 21:48:36 -0400
From:	Bobby Powers <bobbypowers@...il.com>
To:	Jeff Mahoney <jeffm@...e.de>
Cc:	Ilya Dryomov <idryomov@...il.com>,
	Chris Mason <chris.mason@...cle.com>,
	Andi Kleen <ak@...ux.intel.com>, linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Btrfs: remove BUG_ON from get_restripe_target

On Wed, Apr 4, 2012 at 9:19 PM, Bobby Powers <bobbypowers@...il.com> wrote:
> On Wed, Apr 4, 2012 at 8:46 PM, Jeff Mahoney <jeffm@...e.de> wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
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>> On 04/04/2012 04:19 PM, Bobby Powers wrote:
>>> spin_is_locked always returns 0 on non-SMP systems, which causes
>>> btrfs to fail the mount.  There is documentation pending as to why
>>> checking for spin_is_locked is a bad idea:
>>>
>>> https://lkml.org/lkml/2012/3/27/413
>>>
>>> As this was the only location in fs/btrfs/extent-tree.c that did
>>> lock-correctness checking in a BUG_ON, simply remove it.
>>>
>>> Signed-off-by: Bobby Powers <bobbypowers@...il.com> CC: Ilya
>>> Dryomov <idryomov@...il.com> CC: Chris Mason
>>> <chris.mason@...cle.com> CC: Andi Kleen <ak@...ux.intel.com> CC:
>>> linux-btrfs@...r.kernel.org CC: linux-kernel@...r.kernel.org ---
>>> fs/btrfs/extent-tree.c |    3 --- 1 file changed, 3 deletions(-)
>>>
>>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index
>>> a844204..c98b073 100644 --- a/fs/btrfs/extent-tree.c +++
>>> b/fs/btrfs/extent-tree.c @@ -3158,9 +3158,6 @@ static u64
>>> get_restripe_target(struct btrfs_fs_info *fs_info, u64 flags)
>>> struct btrfs_balance_control *bctl = fs_info->balance_ctl; u64
>>> target = 0;
>>>
>>> -     BUG_ON(!mutex_is_locked(&fs_info->volume_mutex) && -
>>> !spin_is_locked(&fs_info->balance_lock)); - if (!bctl) return 0;
>>>
>>
>> Why not replace both of these with lockdep_assert_held as Andi
>> suggested in his doc?
>
> The complication here is that the existing statement was asserting
> that _either_ volume_mutex was held _or_ balance_lock was held -
> lockdep_assert_held is defined as:
>
> #define lockdep_assert_held(l)  WARN_ON(debug_locks && !lockdep_is_held(l))

Well, I guess it works fine if lockdep.h defines lockdep_is_held(l)
for the !LOCKDEP case:

       BUG_ON(debug_locks && !lockdep_is_held(&fs_info->volume_mutex) &&
              !lockdep_is_held(&fs_info->balance_lock));

> which doesn't map to the existing logic.  Although I could be missing something.
>
> Sorry for the double email, forgot to turn off html mail initially.
>
> yours,
> Bobby
>
>> - -Jeff
>>
>> - --
>> Jeff Mahoney
>> SUSE Labs
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