linux-kernel - Re: [GIT PULL] Keep synchronize_rcu() from enabling irqs in early boot

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Message-ID: <20221024200446.GD5600@paulmck-ThinkPad-P17-Gen-1>
Date:   Mon, 24 Oct 2022 13:04:46 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        rcu@...r.kernel.org, kernel-team@...com, rostedt@...dmis.org
Subject: Re: [GIT PULL] Keep synchronize_rcu() from enabling irqs in early
 boot

On Mon, Oct 24, 2022 at 12:40:01PM -0700, Linus Torvalds wrote:
> On Mon, Oct 24, 2022 at 9:54 AM Paul E. McKenney <paulmck@...nel.org> wrote:
> >
> > This pull request contains a commit that fixes bf95b2bc3e42 ("rcu: Switch
> > polled grace-period APIs to ->gp_seq_polled"), which could incorrectly
> > leave interrupts enabled after an early-boot call to synchronize_rcu().
> 
> Minor stylistic nit-pick - please try to keep the commit tags
> together, ie the "Fixes:" tags goes with Reported-by: tags and
> sign-offs etc..

Please accept my apologies for my confusion!

Please see below for a pull request for a better-formatted commit.

							Thanx, Paul

------------------------------------------------------------------------

This pull request fixes a merge-window regression noted by Steve Rostedt.

The following changes since commit 9abf2313adc1ca1b6180c508c25f22f9395cc780:

  Linux 6.1-rc1 (2022-10-16 15:36:24 -0700)

are available in the Git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git tags/rcu-urgent.2022.10.24a

for you to fetch changes up to c216e5557395092a1a30ddb2be8ab924b0364585:

  rcu: Keep synchronize_rcu() from enabling irqs in early boot (2022-10-24 12:55:37 -0700)

----------------------------------------------------------------
Urgent RCU pull request for v6.1

This pull request contains a commit that fixes bf95b2bc3e42 ("rcu: Switch
polled grace-period APIs to ->gp_seq_polled"), which could incorrectly
leave interrupts enabled after an early-boot call to synchronize_rcu().
Such synchronize_rcu() calls must acquire leaf rcu_node locks in order to
properly interact with polled grace periods, but the code did not take
into account the possibility of synchronize_rcu() being invoked from
the portion of the boot sequence during which interrupts are disabled.
This commit therefore switches the lock acquisition and release from
irq to irqsave/irqrestore.

----------------------------------------------------------------
Paul E. McKenney (1):
      rcu: Keep synchronize_rcu() from enabling irqs in early boot

 kernel/rcu/tree.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)