linux-kernel - Re: [PATCH 2/6] lightnvm: pblk: protect line bitmap while submitting meta io

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Date:   Mon, 25 Sep 2017 12:14:51 +0200
From:   Matias Bjørling <mb@...htnvm.io>
To:     Javier González <jg@...htnvm.io>,
        Rakesh Pandit <rakesh@...era.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] lightnvm: pblk: protect line bitmap while submitting
 meta io

On 09/22/2017 10:49 AM, Javier González wrote:
>> On 21 Sep 2017, at 13.26, Rakesh Pandit <rakesh@...era.com> wrote:
>>
>> It seems pblk_dealloc_page would race against pblk_alloc_pages for
>> line bitmap for sector allocation.  The chances are very low but might
>> as well protect the bitmap properly.  It's not even in fast path.
>>
>> Signed-off-by: Rakesh Pandit <rakesh@...era.com>
>> ---
>> drivers/lightnvm/pblk-core.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/lightnvm/pblk-core.c b/drivers/lightnvm/pblk-core.c
>> index a230125..b92eabc 100644
>> --- a/drivers/lightnvm/pblk-core.c
>> +++ b/drivers/lightnvm/pblk-core.c
>> @@ -502,12 +502,14 @@ void pblk_dealloc_page(struct pblk *pblk, struct pblk_line *line, int nr_secs)
>> 	u64 addr;
>> 	int i;
>>
>> +	spin_lock(&line->lock);
>> 	addr = find_next_zero_bit(line->map_bitmap,
>> 					pblk->lm.sec_per_line, line->cur_sec);
>> 	line->cur_sec = addr - nr_secs;
>>
>> 	for (i = 0; i < nr_secs; i++, line->cur_sec--)
>> 		WARN_ON(!test_and_clear_bit(line->cur_sec, line->map_bitmap));
>> +	spin_lock(&line->lock);
>> }
>>
>> u64 __pblk_alloc_page(struct pblk *pblk, struct pblk_line *line, int nr_secs)
>> --
>> 2.5.0
> 
> Looks good. The reason not to have locks here was that the caller is
> always on the write thread - who did the allocation -, since it is error
> handling. So there is no protection needed. In any case, it is better to
> have it since it is implemented as a helper function.
> 
> 
> Reviewed-by: Javier González <javier@...xlabs.com>
> 

Thanks, I picked it up.