The patch titled
Subject: kernel/watchdog: flush all printk nmi buffers when hardlockup detected
has been added to the -mm tree. Its filename is
kernel-watchdog-flush-all-printk-nmi-buffers-when-hardlockup-detected.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/kernel-watchdog-flush-all-printk-nmi-buffers-when-hardlockup-detected.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/kernel-watchdog-flush-all-printk-nmi-buffers-when-hardlockup-detected.patch
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------------------------------------------------------
From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Subject: kernel/watchdog: flush all printk nmi buffers when hardlockup detected
In NMI context printk() could save messages into per-cpu buffers and
schedule flush by irq_work when IRQ are unblocked. This means message
about hardlockup appears in kernel log only when/if lockup is gone.
Comment in irq_work_queue_on() states that remote IPI aren't NMI safe thus
printk() cannot schedule flush work to another cpu.
This patch adds simple atomic counter of detected hardlockups and flushes
all per-cpu printk buffers in context softlockup watchdog at any other cpu
when it sees changes of this counter.
Link: http://lkml.kernel.org/r/158132813726.1980.17382047082627699898.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Cc: Dmitry Monakhov <dmtrmonakhov@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/nmi.h | 1 +
kernel/watchdog.c | 22 ++++++++++++++++++++++
kernel/watchdog_hld.c | 1 +
3 files changed, 24 insertions(+)
--- a/include/linux/nmi.h~kernel-watchdog-flush-all-printk-nmi-buffers-when-hardlockup-detected
+++ a/include/linux/nmi.h
@@ -84,6 +84,7 @@ static inline void reset_hung_task_detec
#if defined(CONFIG_HARDLOCKUP_DETECTOR)
extern void hardlockup_detector_disable(void);
extern unsigned int hardlockup_panic;
+extern atomic_t hardlockup_detected;
#else
static inline void hardlockup_detector_disable(void) {}
#endif
--- a/kernel/watchdog.c~kernel-watchdog-flush-all-printk-nmi-buffers-when-hardlockup-detected
+++ a/kernel/watchdog.c
@@ -92,6 +92,26 @@ static int __init hardlockup_all_cpu_bac
}
__setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
# endif /* CONFIG_SMP */
+
+atomic_t hardlockup_detected = ATOMIC_INIT(0);
+
+static inline void flush_hardlockup_messages(void)
+{
+ static atomic_t flushed = ATOMIC_INIT(0);
+
+ /* flush messages from hard lockup detector */
+ if (atomic_read(&hardlockup_detected) != atomic_read(&flushed)) {
+ atomic_set(&flushed, atomic_read(&hardlockup_detected));
+ printk_safe_flush();
+ }
+}
+
+#else /* CONFIG_HARDLOCKUP_DETECTOR */
+
+static inline void flush_hardlockup_messages(void)
+{
+}
+
#endif /* CONFIG_HARDLOCKUP_DETECTOR */
/*
@@ -370,6 +390,8 @@ static enum hrtimer_restart watchdog_tim
/* kick the hardlockup detector */
watchdog_interrupt_count();
+ flush_hardlockup_messages();
+
/* kick the softlockup detector */
if (completion_done(this_cpu_ptr(&softlockup_completion))) {
reinit_completion(this_cpu_ptr(&softlockup_completion));
--- a/kernel/watchdog_hld.c~kernel-watchdog-flush-all-printk-nmi-buffers-when-hardlockup-detected
+++ a/kernel/watchdog_hld.c
@@ -154,6 +154,7 @@ static void watchdog_overflow_callback(s
if (hardlockup_panic)
nmi_panic(regs, "Hard LOCKUP");
+ atomic_inc(&hardlockup_detected);
__this_cpu_write(hard_watchdog_warn, true);
return;
_
Patches currently in -mm which might be from khlebnikov@xxxxxxxxxxxxxx are
kernel-watchdog-flush-all-printk-nmi-buffers-when-hardlockup-detected.patch
lib-test_lockup-test-module-to-generate-lockups.patch
