linux-kernel - Re: [PATCH] btrfs: add lockdep_assert_held to need_preemptive

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Date:   Thu, 3 Mar 2022 01:25:57 +0100
From:   Niels Dossche <dossche.niels@...il.com>
To:     dsterba@...e.cz, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Johannes Thumshirn <johannes.thumshirn@....com>
Subject: Re: [PATCH] btrfs: add lockdep_assert_held to need_preemptive_reclaim

On 02/03/2022 20:30, David Sterba wrote:
> On Mon, Feb 28, 2022 at 11:52:16PM +0100, Niels Dossche wrote:
>> In a previous patch I extended the locking for member accesses of
>> space_info.
> 
> A reference to another patch would be by a subject or a specific commit
> id (not applicable in this case) or you can write it without any
> reference if the change is standalone. The changelog should describe the
> reason for the change, user visible effects, what can go wrong etc.
> 

I will make sure to do that in the future. Thanks.

>> It was then suggested to also add a lockdep assertion for
>> space_info->lock to need_preemptive_reclaim.
>>
>> Suggested-by: Johannes Thumshirn <johannes.thumshirn@....com>
>> Signed-off-by: Niels Dossche <dossche.niels@...il.com>
>> ---
>>  fs/btrfs/space-info.c | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
>> index 294242c194d8..5464bd168d5b 100644
>> --- a/fs/btrfs/space-info.c
>> +++ b/fs/btrfs/space-info.c
>> @@ -734,9 +734,13 @@ static bool need_preemptive_reclaim(struct btrfs_fs_info *fs_info,
>>  {
>>  	u64 global_rsv_size = fs_info->global_block_rsv.reserved;
>>  	u64 ordered, delalloc;
>> -	u64 thresh = div_factor_fine(space_info->total_bytes, 90);
>> +	u64 thresh;
>>  	u64 used;
>>  
>> +	lockdep_assert_held(&space_info->lock);
>> +
>> +	thresh = div_factor_fine(space_info->total_bytes, 90);
> 
> I'm not sure this is necessary, as this is not locking where the
> initialization would have to be inside. The lockdep assertion is just a
> warning, so it does not matter where the intialization is done, I'd
> prefer to keep it as is.

I understand. Thank you for your feedback. I will send a v2 shortly.