lkml.org 
[lkml]   [2014]   [Apr]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[RFC v2 01/10] sysrq: Implement __handle_sysrq_nolock to avoid recursive locking in kdb
Date
If kdb is triggered using SysRq-g then any use of the sr command results
in the SysRq key table lock being recursively acquired, killing the debug
session. That patch resolves the problem by introducing a _nolock
alternative for __handle_sysrq.

Strictly speaking this approach risks racing on the key table when kdb is
triggered by something other than SysRq-g however in that case any other
CPU involved should release the spin lock before kgdb parks the slave
CPUs.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
---
drivers/tty/sysrq.c | 11 ++++++++---
include/linux/sysrq.h | 1 +
kernel/debug/kdb/kdb_main.c | 2 +-
3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index ce396ec..7b47b2d 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -505,14 +505,12 @@ static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
sysrq_key_table[i] = op_p;
}

-void __handle_sysrq(int key, bool check_mask)
+void __handle_sysrq_nolock(int key, bool check_mask)
{
struct sysrq_key_op *op_p;
int orig_log_level;
int i;
- unsigned long flags;

- spin_lock_irqsave(&sysrq_key_table_lock, flags);
/*
* Raise the apparent loglevel to maximum so that the sysrq header
* is shown to provide the user with positive feedback. We do not
@@ -554,6 +552,13 @@ void __handle_sysrq(int key, bool check_mask)
printk("\n");
console_loglevel = orig_log_level;
}
+}
+
+void __handle_sysrq(int key, bool check_mask)
+{
+ unsigned long flags;
+ spin_lock_irqsave(&sysrq_key_table_lock, flags);
+ __handle_sysrq_nolock(key, check_mask);
spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
}

diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h
index 387fa7d..1d51d64 100644
--- a/include/linux/sysrq.h
+++ b/include/linux/sysrq.h
@@ -44,6 +44,7 @@ struct sysrq_key_op {

void handle_sysrq(int key);
void __handle_sysrq(int key, bool check_mask);
+void __handle_sysrq_nolock(int key, bool check_mask);
int register_sysrq_key(int key, struct sysrq_key_op *op);
int unregister_sysrq_key(int key, struct sysrq_key_op *op);
struct sysrq_key_op *__sysrq_get_key_op(int key);
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 0b097c8..f39f926 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -1924,7 +1924,7 @@ static int kdb_sr(int argc, const char **argv)
if (argc != 1)
return KDB_ARGCOUNT;
kdb_trap_printk++;
- __handle_sysrq(*argv[1], false);
+ __handle_sysrq_nolock(*argv[1], false);
kdb_trap_printk--;

return 0;
--
1.9.0


\
 
 \ /
  Last update: 2014-04-02 18:21    [W:0.365 / U:0.340 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site