From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
LKML <linux-kernel@vger.kernel.org>,
svens@linux.ibm.com
Subject: Re: [WARNING] kernel/rcu/tree.c:1058 rcu_irq_enter+0x15/0x20
Date: Mon, 5 Oct 2020 09:52:06 +0200 [thread overview]
Message-ID: <20201005075206.GI2651@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20201002181313.GM29142@worktop.programming.kicks-ass.net>
On Fri, Oct 02, 2020 at 08:13:13PM +0200, Peter Zijlstra wrote:
> > checks within the irq disabling to get rid of the using cpu pointers within
> > preemptable code warnings
>
> Ah, I think I lost a s/__this_cpu_read/raw_cpu_read/ somewhere. The
> thing is, if we're preemptible/migratable it will be 0 on both CPUs and
> it doesn't matter which 0 we read. If it is !0, IRQs will be disabled
> and we can't get migrated.
Aargh, this isn't in fact correct, and that means I have to revert:
fddf9055a60d ("lockdep: Use raw_cpu_*() for per-cpu variables")
The trouble is that on a bunch of architectures we can read the other
CPUs variable from the new CPU, long after the old CPU has continued
executing things.
So this really needs to be this_cpu_read(). Luckily Sven has already
fixed s390, but let me go audit all the other archs.
next prev parent reply other threads:[~2020-10-05 7:52 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-17 17:16 [WARNING] kernel/rcu/tree.c:1058 rcu_irq_enter+0x15/0x20 Steven Rostedt
2020-09-17 17:18 ` Steven Rostedt
2020-09-25 20:07 ` Steven Rostedt
2020-09-30 18:13 ` Peter Zijlstra
2020-09-30 19:10 ` Steven Rostedt
2020-09-30 19:22 ` Peter Zijlstra
2020-09-30 19:52 ` Steven Rostedt
2020-10-02 9:04 ` Peter Zijlstra
2020-10-02 17:56 ` Steven Rostedt
2020-10-02 18:13 ` Peter Zijlstra
2020-10-05 7:52 ` Peter Zijlstra [this message]
2020-10-05 9:59 ` [PATCH] lockdep: Revert "lockdep: Use raw_cpu_*() for per-cpu variables" Peter Zijlstra
2020-10-07 16:20 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-10-09 7:58 ` tip-bot2 for Peter Zijlstra
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