170 lines
5.5 KiB
Diff
170 lines
5.5 KiB
Diff
From 4cfe99af9a7fab14a52aeff48f057bc66720a6ca Mon Sep 17 00:00:00 2001
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From: Frank Rowand <frank.rowand@am.sony.com>
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Date: Fri, 23 Sep 2011 13:43:12 -0700
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Subject: [PATCH 248/271] sysrq: Allow immediate Magic SysRq output for
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PREEMPT_RT_FULL
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Add a CONFIG option to allow the output from Magic SysRq to be output
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immediately, even if this causes large latencies.
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If PREEMPT_RT_FULL, printk() will not try to acquire the console lock
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when interrupts or preemption are disabled. If the console lock is
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not acquired the printk() output will be buffered, but will not be
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output immediately. Some drivers call into the Magic SysRq code
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with interrupts or preemption disabled, so the output of Magic SysRq
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will be buffered instead of printing immediately if this option is
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not selected.
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Even with this option selected, Magic SysRq output will be delayed
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if the attempt to acquire the console lock fails.
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Signed-off-by: Frank Rowand <frank.rowand@am.sony.com>
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Link: http://lkml.kernel.org/r/4E7CEF60.5020508@am.sony.com
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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[ukleinek: make apply on top of debian/sysrq-mask.patch]
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drivers/tty/serial/cpm_uart/cpm_uart_core.c | 2 +-
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drivers/tty/sysrq.c | 23 +++++++++++++++++++++++
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include/linux/sysrq.h | 5 +++++
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kernel/printk.c | 5 +++--
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lib/Kconfig.debug | 22 ++++++++++++++++++++++
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5 files changed, 54 insertions(+), 3 deletions(-)
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diff --git a/drivers/tty/serial/cpm_uart/cpm_uart_core.c b/drivers/tty/serial/cpm_uart/cpm_uart_core.c
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index b418947..a8b0559 100644
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--- a/drivers/tty/serial/cpm_uart/cpm_uart_core.c
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+++ b/drivers/tty/serial/cpm_uart/cpm_uart_core.c
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@@ -1226,7 +1226,7 @@ static void cpm_uart_console_write(struct console *co, const char *s,
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{
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struct uart_cpm_port *pinfo = &cpm_uart_ports[co->index];
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unsigned long flags;
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- int nolock = oops_in_progress;
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+ int nolock = oops_in_progress || sysrq_in_progress;
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if (unlikely(nolock)) {
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local_irq_save(flags);
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diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
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index 43db715..5219738 100644
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--- a/drivers/tty/sysrq.c
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+++ b/drivers/tty/sysrq.c
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@@ -492,6 +492,23 @@ static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
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sysrq_key_table[i] = op_p;
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}
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+#ifdef CONFIG_MAGIC_SYSRQ_FORCE_PRINTK
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+
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+int sysrq_in_progress;
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+
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+static void set_sysrq_in_progress(int value)
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+{
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+ sysrq_in_progress = value;
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+}
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+
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+#else
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+
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+static void set_sysrq_in_progress(int value)
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+{
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+}
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+
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+#endif
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+
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void __handle_sysrq(int key, bool check_mask)
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{
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struct sysrq_key_op *op_p;
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@@ -500,6 +517,9 @@ void __handle_sysrq(int key, bool check_mask)
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unsigned long flags;
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spin_lock_irqsave(&sysrq_key_table_lock, flags);
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+
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+ set_sysrq_in_progress(1);
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+
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/*
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* Raise the apparent loglevel to maximum so that the sysrq header
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* is shown to provide the user with positive feedback. We do not
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@@ -541,6 +561,9 @@ void __handle_sysrq(int key, bool check_mask)
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printk("\n");
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console_loglevel = orig_log_level;
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}
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+
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+ set_sysrq_in_progress(0);
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+
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spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
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}
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diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h
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index 7faf933..d224c0b 100644
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--- a/include/linux/sysrq.h
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+++ b/include/linux/sysrq.h
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@@ -38,6 +38,11 @@ struct sysrq_key_op {
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int enable_mask;
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};
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+#ifdef CONFIG_MAGIC_SYSRQ_FORCE_PRINTK
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+extern int sysrq_in_progress;
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+#else
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+#define sysrq_in_progress 0
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+#endif
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#ifdef CONFIG_MAGIC_SYSRQ
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/* Generic SysRq interface -- you may call it from any device driver, supplying
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diff --git a/kernel/printk.c b/kernel/printk.c
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index 13ea6a9..9eabbbb 100644
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--- a/kernel/printk.c
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+++ b/kernel/printk.c
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@@ -21,6 +21,7 @@
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#include <linux/tty.h>
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#include <linux/tty_driver.h>
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#include <linux/console.h>
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+#include <linux/sysrq.h>
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#include <linux/init.h>
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#include <linux/jiffies.h>
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#include <linux/nmi.h>
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@@ -834,8 +835,8 @@ static int console_trylock_for_printk(unsigned int cpu, unsigned long flags)
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{
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int retval = 0, wake = 0;
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#ifdef CONFIG_PREEMPT_RT_FULL
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- int lock = !early_boot_irqs_disabled && !irqs_disabled_flags(flags) &&
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- !preempt_count();
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+ int lock = (!early_boot_irqs_disabled && !irqs_disabled_flags(flags) &&
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+ !preempt_count()) || sysrq_in_progress;
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#else
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int lock = 1;
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#endif
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diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
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index c347db3..13a937b 100644
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--- a/lib/Kconfig.debug
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+++ b/lib/Kconfig.debug
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@@ -62,6 +62,28 @@ config MAGIC_SYSRQ
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Specifies the default mask for the allowed SysRq keys. This can be
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used to disable several sensitive keys by default.
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+config MAGIC_SYSRQ_FORCE_PRINTK
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+ bool "Force printk from Magic SysRq"
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+ depends on MAGIC_SYSRQ && PREEMPT_RT_FULL
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+ default n
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+ help
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+ Allow the output from Magic SysRq to be output immediately, even if
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+ this causes large latencies. This can cause performance problems
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+ for real-time processes.
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+
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+ If PREEMPT_RT_FULL, printk() will not try to acquire the console lock
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+ when interrupts or preemption are disabled. If the console lock is
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+ not acquired the printk() output will be buffered, but will not be
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+ output immediately. Some drivers call into the Magic SysRq code
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+ with interrupts or preemption disabled, so the output of Magic SysRq
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+ will be buffered instead of printing immediately if this option is
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+ not selected.
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+
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+ Even with this option selected, Magic SysRq output will be delayed
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+ if the attempt to acquire the console lock fails.
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+
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+ Don't say Y unless you really know what this hack does.
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+
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config STRIP_ASM_SYMS
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bool "Strip assembler-generated symbols during link"
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default n
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--
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1.7.10
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