From: Peter Zijlstra <peterz@infradead.org>
To: Petr Mladek <pmladek@suse.com>
Cc: linyongting@huawei.com, kejinling@huawei.com,
akpm@linux-foundation.org, sergey.senozhatsky@gmail.com,
bp@suse.de, tj@kernel.org, treding@nvidia.com,
linux-kernel@vger.kernel.org, leisure.wang@huawei.com
Subject: Re: [PATCH] printk: Fix spinlock deadlock in printk reenty
Date: Wed, 30 Nov 2016 12:30:49 +0100 [thread overview]
Message-ID: <20161130113049.GN3045@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20161130105653.GF24060@pathway.suse.cz>
On Wed, Nov 30, 2016 at 11:56:53AM +0100, Petr Mladek wrote:
> On Wed 2016-11-30 15:15:19, linyongting@huawei.com wrote:
> > In arm, arm64, x86 or other architecture, spinlock variable
x86 no longer uses ticket locks.
> > The solution is that In function zap_locks(), replace
> > raw_spin_lock_init(&logbuf_lock) with raw_spin_unlock(&logbuf_lock),
That's broken too. Imagine the CPU that actually holds the lock then
_also_ doing an unlock. At that point the tail is ahead of the head and
you're also up some creek without no paddle.
Note that I ran into all these scenarios many years ago..
> Another solution would be to make printk() to ignore locks
> when Oops is in progress. It was somewhere suggested by Peter
> Zijlstra. Well, it might cause some problems as well when
> there are more CPUs still running and printing.
Ignoring is the only option. There is no way to fudge the lock state and
live to tell about it.
next prev parent reply other threads:[~2016-11-30 11:31 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-30 7:15 [PATCH] printk: Fix spinlock deadlock in printk reenty linyongting
2016-11-30 10:56 ` Petr Mladek
2016-11-30 11:30 ` Peter Zijlstra [this message]
2016-11-30 20:51 ` Andrew Morton
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