linux-kernel - Re: [PATCH 08/10] srcu: Add __srcu_clone_read

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Message-ID: <20240710120522.GG28838@noisy.programming.kicks-ass.net>
Date: Wed, 10 Jul 2024 14:05:22 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: mingo@...nel.org, andrii@...nel.org, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org, mhiramat@...nel.org, oleg@...hat.com,
	jolsa@...nel.org, clm@...a.com, paulmck@...nel.org
Subject: Re: [PATCH 08/10] srcu: Add __srcu_clone_read_lock()

On Wed, Jul 10, 2024 at 12:02:02PM +0200, Peter Zijlstra wrote:
> On Tue, Jul 09, 2024 at 10:48:39PM -0700, Boqun Feng wrote:
> > On Mon, Jul 08, 2024 at 11:12:49AM +0200, Peter Zijlstra wrote:
> > > In order to support carrying an srcu_read_lock() section across fork,
> > > where both the parent and child process will do: srcu_read_unlock(),
> > > it is needed to account for the extra decrement with an extra
> > > increment at fork time.
> > > 
> > 
> > We also need to dup the per-task lock held stack in order to maintain
> > consistent data for lockdep, right?
> 
> Urgh, not the whole stack, but yeah, we need to stick an entry on there.
> 
> Let me see if I can frob that somehow.

Ah, since this all is across userspace, the easiest solution it so also
use __srcu_read_{,un}lock() and ignore lockdep entirely.