[PATCH/RFC] sysrq: updating console_loglevel

[Randy.Dunlap]

Chris,
Here's a patch for you to try.  It creates a safe method for
sysrq handlers to modify console_loglevel, which I suspect is
why you were not seeing messages on the serial console.

Please report back on your testing.
Thanks.
---

From: Randy Dunlap <rdunlap@xxxxxxxxxxxx>

Some sysrq handlers modify the console_loglevel variable,
but when they do so, some of their own messages may be lost
(not logged, esp. on serial console).

This patch introduces a way for console_loglevel to be
modified safely by the sysrq handlers.  The new value is not
set until the sysrq handler complets and returns.

Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxx>
---

 drivers/char/sysrq.c |   16 +++++++++-------
 1 files changed, 9 insertions(+), 7 deletions(-)

diff -Naurp linux-2613-rc2/drivers/char/sysrq.c~fix_loglevel linux-2613-rc2/drivers/char/sysrq.c
--- linux-2613-rc2/drivers/char/sysrq.c~fix_loglevel	2005-07-09 13:55:01.000000000 -0700
+++ linux-2613-rc2/drivers/char/sysrq.c	2005-09-25 21:31:12.000000000 -0700
@@ -41,6 +41,7 @@
 
 /* Whether we react on sysrq keys or just ignore them */
 int sysrq_enabled = 1;
+static int next_log_level;
 
 /* Loglevel sysrq handler */
 static void sysrq_handle_loglevel(int key, struct pt_regs *pt_regs,
@@ -50,7 +51,7 @@ static void sysrq_handle_loglevel(int ke
 	i = key - '0';
 	console_loglevel = 7;
 	printk("Loglevel set to %d\n", i);
-	console_loglevel = i;
+	next_log_level = i;
 }	
 static struct sysrq_key_op sysrq_loglevel_op = {
 	.handler	= sysrq_handle_loglevel,
@@ -217,7 +218,7 @@ static void sysrq_handle_term(int key, s
 			      struct tty_struct *tty) 
 {
 	send_sig_all(SIGTERM);
-	console_loglevel = 8;
+	next_log_level = 8;
 }
 static struct sysrq_key_op sysrq_term_op = {
 	.handler	= sysrq_handle_term,
@@ -248,7 +249,7 @@ static void sysrq_handle_kill(int key, s
 			      struct tty_struct *tty) 
 {
 	send_sig_all(SIGKILL);
-	console_loglevel = 8;
+	next_log_level = 8;
 }
 static struct sysrq_key_op sysrq_kill_op = {
 	.handler	= sysrq_handle_kill,
@@ -371,12 +372,11 @@ void __sysrq_put_key_op (int key, struct
 void __handle_sysrq(int key, struct pt_regs *pt_regs, struct tty_struct *tty, int check_mask)
 {
 	struct sysrq_key_op *op_p;
-	int orig_log_level;
 	int i, j;
 	unsigned long flags;
 
 	spin_lock_irqsave(&sysrq_key_table_lock, flags);
-	orig_log_level = console_loglevel;
+	next_log_level = console_loglevel;
 	console_loglevel = 7;
 	printk(KERN_INFO "SysRq : ");
 
@@ -387,8 +387,10 @@ void __handle_sysrq(int key, struct pt_r
 		if (!check_mask || sysrq_enabled == 1 ||
 		    (sysrq_enabled & op_p->enable_mask)) {
 			printk ("%s\n", op_p->action_msg);
-			console_loglevel = orig_log_level;
+			/* handlers may change console_loglevel,
+			 * but now they do this by setting <next_log_level> */
 			op_p->handler(key, pt_regs, tty);
+			console_loglevel = next_log_level;
 		}
 		else
 			printk("This sysrq operation is disabled.\n");
@@ -402,7 +404,7 @@ void __handle_sysrq(int key, struct pt_r
 				printk ("%s ", sysrq_key_table[i]->help_msg);
 		}
 		printk ("\n");
-		console_loglevel = orig_log_level;
+		console_loglevel = next_log_level;
 	}
 	spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
 }
-
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