linux-kernel - Re: [PATCH v3 05/11] md/raid5-cache: Drop RCU usage of conf->log

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Message-ID: <YpmteYBT71dYY7t0@infradead.org>
Date:   Thu, 2 Jun 2022 23:43:05 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
        Song Liu <song@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Donald Buczek <buczek@...gen.mpg.de>,
        Guoqing Jiang <guoqing.jiang@...ux.dev>,
        Xiao Ni <xni@...hat.com>, Stephen Bates <sbates@...thlin.com>,
        Martin Oliveira <Martin.Oliveira@...eticom.com>,
        David Sloan <David.Sloan@...eticom.com>
Subject: Re: [PATCH v3 05/11] md/raid5-cache: Drop RCU usage of conf->log

On Thu, Jun 02, 2022 at 12:18:11PM -0600, Logan Gunthorpe wrote:
> The only place that uses RCU to access conf->log is in
> r5l_log_disk_error(). This function is mostly used in the IO path
> and once with mddev_lock() held in raid5_change_consistency_policy().
> 
> It is known that the IO will be suspended before the log is freed and
> r5l_log_exit() is called with the mddev_lock() held.
> 
> This should mean that conf->log can not be freed while the function is
> being called, so the RCU protection is not necessary. Drop the
> rcu_read_lock() as well as the synchronize_rcu() and
> rcu_assign_pointer() usage.

Looks good:

Reviewed-by: Christoph Hellwig <hch@....de>