linux-kernel - Re: [PATCH] lightnvm: pblk: fix race condition on metadata I/O

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Message-ID: <fbe93d3b-31d5-608c-e9fc-c77510763462@lightnvm.io>
Date:   Fri, 17 Aug 2018 12:37:02 +0200
From:   Matias Bjørling <mb@...htnvm.io>
To:     javier@...igon.com
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        javier@...xlabs.com
Subject: Re: [PATCH] lightnvm: pblk: fix race condition on metadata I/O

On 08/17/2018 12:22 PM, Javier González wrote:
> In pblk, when a new line is allocated, metadata for the previously
> written line is scheduled. This is done through a fixed memory region
> that is shared through time and contexts across different lines and
> therefore protected by a lock. Unfortunately, this lock is not properly
> covering all the metadata used for sharing this memory regions,
> resulting on a race condition.
> 
> This patch fixes this race condition by protecting this metadata
> properly.
> 
> Fixes: dd2a43437337 ("lightnvm: pblk: sched. metadata on write thread")
> 
> Signed-off-by: Javier González <javier@...xlabs.com>
> ---
>   drivers/lightnvm/pblk-write.c | 14 +++++++-------
>   1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/lightnvm/pblk-write.c b/drivers/lightnvm/pblk-write.c
> index 508c63701eda..df99c45778d4 100644
> --- a/drivers/lightnvm/pblk-write.c
> +++ b/drivers/lightnvm/pblk-write.c
> @@ -417,12 +417,11 @@ int pblk_submit_meta_io(struct pblk *pblk, struct pblk_line *meta_line)
>   			rqd->ppa_list[i] = addr_to_gen_ppa(pblk, paddr, id);
>   	}
>   
> +	spin_lock(&l_mg->close_lock);
>   	emeta->mem += rq_len;
> -	if (emeta->mem >= lm->emeta_len[0]) {
> -		spin_lock(&l_mg->close_lock);
> +	if (emeta->mem >= lm->emeta_len[0])
>   		list_del(&meta_line->list);
> -		spin_unlock(&l_mg->close_lock);
> -	}
> +	spin_unlock(&l_mg->close_lock);
>   
>   	pblk_down_page(pblk, rqd->ppa_list, rqd->nr_ppas);
>   
> @@ -491,14 +490,15 @@ static struct pblk_line *pblk_should_submit_meta_io(struct pblk *pblk,
>   	struct pblk_line *meta_line;
>   
>   	spin_lock(&l_mg->close_lock);
> -retry:
>   	if (list_empty(&l_mg->emeta_list)) {
>   		spin_unlock(&l_mg->close_lock);
>   		return NULL;
>   	}
>   	meta_line = list_first_entry(&l_mg->emeta_list, struct pblk_line, list);
> -	if (meta_line->emeta->mem >= lm->emeta_len[0])
> -		goto retry;
> +	if (meta_line->emeta->mem >= lm->emeta_len[0]) {
> +		spin_unlock(&l_mg->close_lock);
> +		return NULL;
> +	} >   	spin_unlock(&l_mg->close_lock);
>   
>   	if (!pblk_valid_meta_ppa(pblk, meta_line, data_rqd))
> 

Thanks. Applied for 4.20.