linux-kernel - Re: [PATCH v9 3/7] srcu: Fix invoke_rcu

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Date:   Tue, 3 Nov 2020 10:07:38 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Marco Elver <elver@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        "Uladzislau Rezki (Sony)" <urezki@...il.com>, fweisbec@...il.com,
        neeraj.iitr10@...il.com
Subject: Re: [PATCH v9 3/7] srcu: Fix invoke_rcu_callbacks() segcb length
 adjustment

On Tue, Nov 03, 2020 at 03:47:14PM +0100, Frederic Weisbecker wrote:
> On Tue, Nov 03, 2020 at 09:25:59AM -0500, Joel Fernandes (Google) wrote:
> > With earlier patches, the negative counting of the unsegmented list
> > cannot be used to adjust the segmented one. To fix this, sample the
> > unsegmented length in advance, and use it after CB execution to adjust
> > the segmented list's length.
> > 
> > Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
> > Suggested-by: Frederic Weisbecker <frederic@...nel.org>
> > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> 
> This breaks bisection, you need to either fix up the previous patch
> by adding this diff inside or better yet: expand what you did
> in "rcu/tree: Make rcu_do_batch count how many callbacks were executed"
> to also handle srcu before introducing the segcb count.

Since doing the latter is a lot more tedious and I want to get reviewing
other's RCU patches today :) , I just squashed the suggestion into the
counters patch to fix bissection:
https://git.kernel.org/pub/scm/linux/kernel/git/jfern/linux.git/commit/?h=rcu/segcb-counts&id=595e3a65eeef109cb8fcbfcc114fd3ea2064b873

Hope that's Ok. Also, so that I don't have to resend everything, here is the
final branch if Paul wants to take it:
git://git.kernel.org/pub/scm/linux/kernel/git/jfern/linux.git (branch rcu/segcb-counts)

Thank you for your time, Frederick!

 - Joel