[RFC PATCH] sysrq: don't hold the sysrq_key_table_lock during the handler

From: Xiaotian Feng
Date: Mon Jul 26 2010 - 05:55:12 EST

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@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Neil Horman <nhorman@xxxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
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)
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)

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