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Date: Fri, 23 Sep 2011 13:43:12 -0700
From: Frank Rowand <frank.rowand@...sony.com>
To: "tglx@...utronix.de" <tglx@...utronix.de>
CC: <linux-rt-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH V3] preempt-rt: allow immediate Magic SysRq output for PREEMPT_RT_FULL
(Resend, adding CCs.)
Change from V2 to V3:
- Put sysrq_in_progress in sysrq.h instead of kernel.h
- Did not need to test for sysrq_in_progress in most drivers because
they already test for port->sysrq. The oddball driver is
drivers/tty/serial/cpm_uart/cpm_uart_core.c, which does not test
for port->sysrq.
Add a CONFIG option to allow the output from Magic SysRq to be output
immediately, even if this causes large latencies.
If PREEMPT_RT_FULL, printk() will not try to acquire the console lock
when interrupts or preemption are disabled. If the console lock is
not acquired the printk() output will be buffered, but will not be
output immediately. Some drivers call into the Magic SysRq code
with interrupts or preemption disabled, so the output of Magic SysRq
will be buffered instead of printing immediately if this option is
not selected.
Even with this option selected, Magic SysRq output will be delayed
if the attempt to acquire the console lock fails.
Signed-off-by: Frank Rowand <frank.rowand@...sony.com>
---
drivers/tty/serial/cpm_uart/cpm_uart_core.c | 2 1 + 1 - 0 !
drivers/tty/sysrq.c | 23 23 + 0 - 0 !
include/linux/sysrq.h | 5 5 + 0 - 0 !
kernel/printk.c | 5 3 + 2 - 0 !
lib/Kconfig.debug | 22 22 + 0 - 0 !
5 files changed, 54 insertions(+), 3 deletions(-)
Index: b/drivers/tty/sysrq.c
===================================================================
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -492,6 +492,23 @@ static void __sysrq_put_key_op(int key,
sysrq_key_table[i] = op_p;
}
+#ifdef CONFIG_MAGIC_SYSRQ_FORCE_PRINTK
+
+int sysrq_in_progress;
+
+static void set_sysrq_in_progress(int value)
+{
+ sysrq_in_progress = value;
+}
+
+#else
+
+static void set_sysrq_in_progress(int value)
+{
+}
+
+#endif
+
void __handle_sysrq(int key, bool check_mask)
{
struct sysrq_key_op *op_p;
@@ -500,6 +517,9 @@ void __handle_sysrq(int key, bool check_
unsigned long flags;
spin_lock_irqsave(&sysrq_key_table_lock, flags);
+
+ set_sysrq_in_progress(1);
+
/*
* Raise the apparent loglevel to maximum so that the sysrq header
* is shown to provide the user with positive feedback. We do not
@@ -541,6 +561,9 @@ void __handle_sysrq(int key, bool check_
printk("\n");
console_loglevel = orig_log_level;
}
+
+ set_sysrq_in_progress(0);
+
spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
}
Index: b/kernel/printk.c
===================================================================
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -21,6 +21,7 @@
#include <linux/tty.h>
#include <linux/tty_driver.h>
#include <linux/console.h>
+#include <linux/sysrq.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/nmi.h>
@@ -831,8 +832,8 @@ static int console_trylock_for_printk(un
__releases(&logbuf_lock)
{
#ifdef CONFIG_PREEMPT_RT_FULL
- int lock = !early_boot_irqs_disabled && !irqs_disabled_flags(flags) &&
- !preempt_count();
+ int lock = (!early_boot_irqs_disabled && !irqs_disabled_flags(flags) &&
+ !preempt_count()) || sysrq_in_progress;
#else
int lock = 1;
#endif
Index: b/drivers/tty/serial/cpm_uart/cpm_uart_core.c
===================================================================
--- a/drivers/tty/serial/cpm_uart/cpm_uart_core.c
+++ b/drivers/tty/serial/cpm_uart/cpm_uart_core.c
@@ -1225,7 +1225,7 @@ static void cpm_uart_console_write(struc
{
struct uart_cpm_port *pinfo = &cpm_uart_ports[co->index];
unsigned long flags;
- int nolock = oops_in_progress;
+ int nolock = oops_in_progress || sysrq_in_progress;
if (unlikely(nolock)) {
local_irq_save(flags);
Index: b/lib/Kconfig.debug
===================================================================
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -62,6 +62,28 @@ config MAGIC_SYSRQ
keys are documented in <file:Documentation/sysrq.txt>. Don't say Y
unless you really know what this hack does.
+config MAGIC_SYSRQ_FORCE_PRINTK
+ bool "Force printk from Magic SysRq"
+ depends on MAGIC_SYSRQ && PREEMPT_RT_FULL
+ default n
+ help
+ Allow the output from Magic SysRq to be output immediately, even if
+ this causes large latencies. This can cause performance problems
+ for real-time processes.
+
+ If PREEMPT_RT_FULL, printk() will not try to acquire the console lock
+ when interrupts or preemption are disabled. If the console lock is
+ not acquired the printk() output will be buffered, but will not be
+ output immediately. Some drivers call into the Magic SysRq code
+ with interrupts or preemption disabled, so the output of Magic SysRq
+ will be buffered instead of printing immediately if this option is
+ not selected.
+
+ Even with this option selected, Magic SysRq output will be delayed
+ if the attempt to acquire the console lock fails.
+
+ Don't say Y unless you really know what this hack does.
+
config STRIP_ASM_SYMS
bool "Strip assembler-generated symbols during link"
default n
Index: b/include/linux/sysrq.h
===================================================================
--- a/include/linux/sysrq.h
+++ b/include/linux/sysrq.h
@@ -38,6 +38,11 @@ struct sysrq_key_op {
int enable_mask;
};
+#ifdef CONFIG_MAGIC_SYSRQ_FORCE_PRINTK
+extern int sysrq_in_progress;
+#else
+#define sysrq_in_progress 0
+#endif
#ifdef CONFIG_MAGIC_SYSRQ
/* Generic SysRq interface -- you may call it from any device driver, supplying
--
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