linux-kernel - Re: [PATCH 1/4] block/part_stat: remove rcu_read_lock() from part_stat

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Date:   Mon, 4 May 2020 07:00:44 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 1/4] block/part_stat: remove rcu_read_lock() from
 part_stat_lock()

On Mon, May 04, 2020 at 04:29:29PM +0300, Konstantin Khlebnikov wrote:
> RCU lock is required only in blk_account_io_start() to lookup partition.
> After that request holds reference to related hd_struct.
> 
> Replace get_cpu() with preempt_disable() - returned cpu index is unused.
> 
> Non-SMP case also needs preempt_disable, otherwise statistics update could
> be non-atomic. Previously that was provided by rcu_read_lock().
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>

Looks good,

Signed-off-by: Christoph Hellwig <hch@....de>

although I wonder if we should just kill off part_stat_lock and
part_stat_unlock.