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

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Message-Id: <A1244F27-AE62-433A-AFC2-5F40E8B96B53@lightnvm.io>
Date:   Fri, 22 Sep 2017 10:49:01 +0200
From:   Javier González <jg@...htnvm.io>
To:     Rakesh Pandit <rakesh@...era.com>
Cc:     Matias Bjørling <mb@...htnvm.io>,
        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 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>


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