linux-kernel - Re: [PATCH 1/2] bdi: make sure congestion states are clear on free

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Date:   Tue, 6 Feb 2018 17:19:14 +0100
From:   Jan Kara <jack@...e.cz>
To:     Tejun Heo <tj@...nel.org>
Cc:     Jens Axboe <axboe@...nel.dk>, Miklos Szeredi <miklos@...redi.hu>,
        Joshua Miller <joshmiller@...com>, kernel-team@...com,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/2] bdi: make sure congestion states are clear on free

On Fri 02-02-18 09:53:28, Tejun Heo wrote:
> FUSE has a bug where it fails to clear congestion states if a
> connection gets aborted while congested, which can leave
> nr_wb_congested[] stuck until reboot causing wait_iff_congested() to
> wait spuriously.
> 
> While the bdi owner, FUSE, is primarily responsible for clearing
> congestion states before destroying bdi_writebacks, bdi layer can
> ensure that congestion states are not leaked beyond bdi_writeback
> lifecycle.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Joshua Miller <joshmiller@...com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Jan Kara <jack@...e.cz>
> Cc: stable@...r.kernel.org

Looks good. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  include/linux/backing-dev.h |   14 +++++++++++++-
>  mm/backing-dev.c            |    2 +-
>  2 files changed, 14 insertions(+), 2 deletions(-)
> 
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -220,6 +220,18 @@ static inline int bdi_sched_wait(void *w
>  	return 0;
>  }
>  
> +static inline void __wb_congested_free(struct bdi_writeback_congested *congested)
> +{
> +	/*
> +	 * Make sure congestion states are cleared before freeing to avoid
> +	 * nr_wb_congested() corruption which can lead to misbehaving
> +	 * wait_iff_congested().
> +	 */
> +	clear_wb_congested(congested, BLK_RW_SYNC);
> +	clear_wb_congested(congested, BLK_RW_ASYNC);
> +	kfree(congested);
> +}
> +
>  #ifdef CONFIG_CGROUP_WRITEBACK
>  
>  struct bdi_writeback_congested *
> @@ -409,7 +421,7 @@ wb_congested_get_create(struct backing_d
>  static inline void wb_congested_put(struct bdi_writeback_congested *congested)
>  {
>  	if (atomic_dec_and_test(&congested->refcnt))
> -		kfree(congested);
> +		__wb_congested_free(congested);
>  }
>  
>  static inline struct bdi_writeback *wb_find_current(struct backing_dev_info *bdi)
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -509,7 +509,7 @@ void wb_congested_put(struct bdi_writeba
>  	}
>  
>  	spin_unlock_irqrestore(&cgwb_lock, flags);
> -	kfree(congested);
> +	__wb_congested_free(congested);
>  }
>  
>  static void cgwb_release_workfn(struct work_struct *work)
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR