linux-kernel - Re: [RFC PATCH] sysrq: don't hold the sysrq_key_table

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Message-Id: <20100727163622.a19a827b.akpm@linux-foundation.org>
Date:	Tue, 27 Jul 2010 16:36:22 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Xiaotian Feng <dfeng@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Neil Horman <nhorman@...driver.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [RFC PATCH] sysrq: don't hold the sysrq_key_table_lock during
 the handler

On Mon, 26 Jul 2010 17:54:02 +0800
Xiaotian Feng <dfeng@...hat.com> wrote:

> sysrq_key_table_lock is used to protect the sysrq_key_table, make sure
> we get/replace the right operation for the sysrq. But in __handle_sysrq,
> kernel will hold this lock and disable irqs until we finished op_p->handler().
> This may cause false positive watchdog alert when we're doing "show-task-states"
> on a system with many tasks.
> 

It would be better to find a suitable point in an inner loop and add an
appropriately-commented touch_nmi_watchdog().

That way the problem gets fixed for all irqs-off callers, not just one
of them.

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