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

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Date:	Mon, 26 Jul 2010 17:54:02 +0800
From:	Xiaotian Feng <dfeng@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Xiaotian Feng <dfeng@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Neil Horman <nhorman@...driver.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [RFC PATCH] sysrq: don't hold the sysrq_key_table_lock during the handler

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.

Signed-off-by: Xiaotian Feng <dfeng@...hat.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Neil Horman <nhorman@...driver.com>
Cc: "David S. Miller" <davem@...emloft.net>
---
 drivers/char/sysrq.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
index 878ac0c..0856e2e 100644
--- a/drivers/char/sysrq.c
+++ b/drivers/char/sysrq.c
@@ -520,9 +520,11 @@ void __handle_sysrq(int key, struct tty_struct *tty, int check_mask)
 		if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
 			printk("%s\n", op_p->action_msg);
 			console_loglevel = orig_log_level;
+			spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
 			op_p->handler(key, tty);
 		} else {
 			printk("This sysrq operation is disabled.\n");
+			spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
 		}
 	} else {
 		printk("HELP : ");
@@ -541,8 +543,8 @@ void __handle_sysrq(int key, struct tty_struct *tty, int check_mask)
 		}
 		printk("\n");
 		console_loglevel = orig_log_level;
+		spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
 	}
-	spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
 }
 
 void handle_sysrq(int key, struct tty_struct *tty)
-- 
1.7.2

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