From: "Paul E. McKenney" <paulmck@kernel.org>
To: Dan Carpenter <dan.carpenter@linaro.org>
Cc: dwmw@amazon.co.uk, rcu@vger.kernel.org
Subject: Re: [bug report] rcu: Kill rnp->ofl_seq and use only rcu_state.ofl_lock for exclusion
Date: Wed, 8 May 2024 10:32:43 -0700 [thread overview]
Message-ID: <e775bd83-dfa3-4f09-9539-e0e655feda08@paulmck-laptop> (raw)
In-Reply-To: <edfea2ff-d73e-48aa-83db-96daba77c500@moroto.mountain>
On Wed, May 08, 2024 at 05:55:38PM +0300, Dan Carpenter wrote:
> On Wed, May 08, 2024 at 07:33:38AM -0700, Paul E. McKenney wrote:
> > On Wed, May 08, 2024 at 03:29:12PM +0300, Dan Carpenter wrote:
> > > Hello David Woodhouse,
> > >
> > > Commit 82980b1622d9 ("rcu: Kill rnp->ofl_seq and use only
> > > rcu_state.ofl_lock for exclusion") from Feb 16, 2021 (linux-next),
> > > leads to the following Smatch static checker warning:
> > >
> > > kernel/rcu/tree.c:1844 rcu_gp_init()
> > > warn: mixing irq and irqsave
> >
> > There are actually cases where this does make sense, one example being
> > where some called function (for example, rcu_report_qs_rnp() below)
> > needs a flags argument.
> >
>
> I only found one false positive which was kind of related to that in
> __run_hrtimer().
>
> 1643
> 1644 static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base,
> 1645 struct hrtimer_clock_base *base,
> 1646 struct hrtimer *timer, ktime_t *now,
> 1647 unsigned long flags) __must_hold(&cpu_base->lock)
> ^^^^^
>
> 1648 {
> ....
>
> 1678 /*
> 1679 * The timer is marked as running in the CPU base, so it is
> 1680 * protected against migration to a different CPU even if the lock
> 1681 * is dropped.
> 1682 */
> 1683 raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
> ^^^^^
> We potentially enable IRQs.
>
> 1684 trace_hrtimer_expire_entry(timer, now);
> 1685 expires_in_hardirq = lockdep_hrtimer_enter(timer);
> 1686
> 1687 restart = fn(timer);
> 1688
> 1689 lockdep_hrtimer_exit(expires_in_hardirq);
> 1690 trace_hrtimer_expire_exit(timer);
> 1691 raw_spin_lock_irq(&cpu_base->lock);
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> Then disable them again.
>
> 1692
>
> Of course the other warnings are mostly not "bugs" because the callers
> haven't disabled IRQs. They're just in need of clean up.
Agreed, and please see below for the proposed cleanup in this case.
Thanx, Paul
------------------------------------------------------------------------
commit 43e96791e7d1605803093b34fb70217fe29ddaeb
Author: Paul E. McKenney <paulmck@kernel.org>
Date: Wed May 8 10:28:43 2024 -0700
rcu: Disable interrupts directly in rcu_gp_init()
Interrupts are enabled in rcu_gp_init(), so this commit switches from
local_irq_save() and local_irq_restore() to local_irq_disable() and
local_irq_enable().
Link: https://lore.kernel.org/all/febb13ab-a4bb-48b4-8e97-7e9f7749e6da@moroto.mountain/
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index d5507ac1bbf19..7560e204198bb 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1841,7 +1841,7 @@ static noinline_for_stack bool rcu_gp_init(void)
WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF);
/* Exclude CPU hotplug operations. */
rcu_for_each_leaf_node(rnp) {
- local_irq_save(flags);
+ local_irq_disable();
arch_spin_lock(&rcu_state.ofl_lock);
raw_spin_lock_rcu_node(rnp);
if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
@@ -1849,7 +1849,7 @@ static noinline_for_stack bool rcu_gp_init(void)
/* Nothing to do on this leaf rcu_node structure. */
raw_spin_unlock_rcu_node(rnp);
arch_spin_unlock(&rcu_state.ofl_lock);
- local_irq_restore(flags);
+ local_irq_enable();
continue;
}
@@ -1886,7 +1886,7 @@ static noinline_for_stack bool rcu_gp_init(void)
raw_spin_unlock_rcu_node(rnp);
arch_spin_unlock(&rcu_state.ofl_lock);
- local_irq_restore(flags);
+ local_irq_enable();
}
rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
next prev parent reply other threads:[~2024-05-08 17:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-08 12:29 [bug report] rcu: Kill rnp->ofl_seq and use only rcu_state.ofl_lock for exclusion Dan Carpenter
2024-05-08 14:33 ` Paul E. McKenney
2024-05-08 14:55 ` Dan Carpenter
2024-05-08 17:32 ` Paul E. McKenney [this message]
2024-05-08 17:38 ` Dan Carpenter
2024-05-08 23:50 ` Paul E. McKenney
2024-05-09 6:46 ` Dan Carpenter
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=e775bd83-dfa3-4f09-9539-e0e655feda08@paulmck-laptop \
--to=paulmck@kernel.org \
--cc=dan.carpenter@linaro.org \
--cc=dwmw@amazon.co.uk \
--cc=rcu@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.