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From: Song Liu <song@kernel.org>
To: Xiao Ni <xni@redhat.com>
Cc: Song Liu <songliubraving@fb.com>,
	Nigel Croxon <ncroxon@redhat.com>,
	linux-raid <linux-raid@vger.kernel.org>
Subject: Re: [PATCH 1/1] md/raid10: Remove rcu_dereference when it doesn't need rcu lock to protect
Date: Sun, 15 Aug 2021 22:22:46 -0700	[thread overview]
Message-ID: <CAPhsuW4Ev3WBqkFBCVE7h4T8mw4N3GyEmT0tp5StdSs+-UpeBw@mail.gmail.com> (raw)
In-Reply-To: <CALTww2-a0jw-LAqsZc8hDY49TqCCEX9KB4J14g2j7tDR3XF+GQ@mail.gmail.com>

On Fri, Aug 13, 2021 at 6:34 PM Xiao Ni <xni@redhat.com> wrote:
>
> Hi Song
>
> It can improve the performance. It needs to add rcu lock when calling
> rcu_dereference.
> Now it has a bug. It doesn't use rcu lock to protect. In the second
> loop, it doesn't need
> to use rcu_dereference when getting rdev. So to resolve this bug, we can remove
> rcu_dereference directly.

In the second loop, we only use rdev and rrdev when bio and repl_bio
exists. So we shouldn't trigger the "bug" in any cases, right?

Please:
1) If you do think this is a bug, add a fix tag, so we can back port to stable.
   (while I still think it is not a real bug).
2) move struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev); to
  under "if (r10_bio->devs[disk].bio)"; and the rrdev ... to "if
(repl_bio)". And add
  a comment there so it is more clear in the code.

Thanks,
Song

  reply	other threads:[~2021-08-16  5:23 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-09  4:01 [PATCH 1/1] md/raid10: Remove rcu_dereference when it doesn't need rcu lock to protect Xiao Ni
2021-08-13 16:49 ` Song Liu
2021-08-14  1:34   ` Xiao Ni
2021-08-16  5:22     ` Song Liu [this message]
2021-08-16  8:58       ` Xiao Ni
2021-08-16  6:35 ` Guoqing Jiang
     [not found]   ` <CALTww2-YhNyKCyMjjviWJ4XmELNUZJonryrJfXtrwP4DU-C1zg@mail.gmail.com>
2021-08-16  9:33     ` Guoqing Jiang
2021-08-18  1:36 Xiao Ni
2021-08-18  1:43 ` Guoqing Jiang
2021-08-18  1:55   ` Xiao Ni

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