From: Qian Cai <cai@redhat.com>
To: Will Deacon <will@kernel.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm64/smp: Move rcu_cpu_starting() earlier
Date: Thu, 29 Oct 2020 09:17:35 -0400 [thread overview]
Message-ID: <4375b3c87d91af36509291ec18e98ed41420ec41.camel@redhat.com> (raw)
In-Reply-To: <20201029091045.GA29890@willie-the-truck>
On Thu, 2020-10-29 at 09:10 +0000, Will Deacon wrote:
> On Wed, Oct 28, 2020 at 02:26:14PM -0400, Qian Cai wrote:
> > The call to rcu_cpu_starting() in secondary_start_kernel() is not early
> > enough in the CPU-hotplug onlining process, which results in lockdep
> > splats as follows:
> >
> > WARNING: suspicious RCU usage
> > -----------------------------
> > kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!!
> >
> > other info that might help us debug this:
> >
> > RCU used illegally from offline CPU!
> > rcu_scheduler_active = 1, debug_locks = 1
> > no locks held by swapper/1/0.
> >
> > Call trace:
> > dump_backtrace+0x0/0x3c8
> > show_stack+0x14/0x60
> > dump_stack+0x14c/0x1c4
> > lockdep_rcu_suspicious+0x134/0x14c
> > __lock_acquire+0x1c30/0x2600
> > lock_acquire+0x274/0xc48
> > _raw_spin_lock+0xc8/0x140
> > vprintk_emit+0x90/0x3d0
> > vprintk_default+0x34/0x40
> > vprintk_func+0x378/0x590
> > printk+0xa8/0xd4
> > __cpuinfo_store_cpu+0x71c/0x868
> > cpuinfo_store_cpu+0x2c/0xc8
> > secondary_start_kernel+0x244/0x318
> >
> > This is avoided by moving the call to rcu_cpu_starting up near the
> > beginning of the secondary_start_kernel() function.
>
> Hmm, it's not really a move though -- we'll end up calling this thing twice
> afaict. It would be better to make sure we've called notify_cpu_starting()
> early enough. Can we do that instead?
Paul mentioned that it is fine to call rcu_cpu_starting() multiple times, and
Peter mentioned that CPU bringup is complicated. Thus, I thought about doing
something safe here.
I tested a bit of patch below which seems fine, but I can't tell for sure if it
is safe. Any suggestion?
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -224,6 +224,7 @@ asmlinkage notrace void secondary_start_kernel(void)
preempt_disable();
trace_hardirqs_off();
+ notify_cpu_starting(cpu);
/*
* If the system has established the capabilities, make sure
@@ -244,7 +245,6 @@ asmlinkage notrace void secondary_start_kernel(void)
/*
* Enable GIC and timers.
*/
- notify_cpu_starting(cpu);
ipi_setup(cpu);
next prev parent reply other threads:[~2020-10-29 13:17 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-28 18:26 [PATCH] arm64/smp: Move rcu_cpu_starting() earlier Qian Cai
2020-10-28 21:00 ` Paul E. McKenney
2020-10-29 9:10 ` Will Deacon
2020-10-29 13:17 ` Qian Cai [this message]
2020-10-30 8:15 ` Will Deacon
2020-10-29 14:09 ` Paul E. McKenney
2020-10-30 16:33 ` Will Deacon
2020-11-05 22:22 ` Will Deacon
2020-11-05 23:02 ` Qian Cai
2020-11-05 23:28 ` Paul E. McKenney
2020-11-06 2:15 ` Qian Cai
2020-11-06 4:07 ` Paul E. McKenney
2020-11-06 10:37 ` Will Deacon
2020-11-06 12:48 ` Qian Cai
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