[PATCH v2 1/4] sys_info: add helper for callers that handle all_bt

[PATCH v2 1/4] sys_info: add helper for callers that handle all_bt

[Bradley Morgan]

Some callers handle SYS_INFO_ALL_BT themselves before calling sys_info().
Add a helper that strips that bit without turning an all_bt only mask into
a kernel_sys_info fallback.

Signed-off-by: Bradley Morgan <include@grrlz.net>
---
Changes since v1:
- New patch for the shared helper suggested by Petr.

 include/linux/sys_info.h |  1 +
 lib/sys_info.c           | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/linux/sys_info.h b/include/linux/sys_info.h
index a5bc3ea3d44b..87a841ec7b6a 100644
--- a/include/linux/sys_info.h
+++ b/include/linux/sys_info.h
@@ -18,6 +18,7 @@
 #define SYS_INFO_BLOCKED_TASKS		0x00000080
 
 void sys_info(unsigned long si_mask);
+void sys_info_without_all_bt(unsigned long si_mask);
 unsigned long sys_info_parse_param(char *str);
 
 #ifdef CONFIG_SYSCTL
diff --git a/lib/sys_info.c b/lib/sys_info.c
index f32a06ec9ed4..6afd4c697633 100644
--- a/lib/sys_info.c
+++ b/lib/sys_info.c
@@ -164,3 +164,18 @@ void sys_info(unsigned long si_mask)
 {
 	__sys_info(si_mask ? : kernel_si_mask);
 }
+
+void sys_info_without_all_bt(unsigned long si_mask)
+{
+	unsigned long dump_mask = si_mask & ~SYS_INFO_ALL_BT;
+
+	/*
+	 * Do not call sys_info() when the caller context required only
+	 * backtraces from all CPUs. Otherwise sys_info() would fall back
+	 * to the generic kernel_si_mask.
+	 */
+	if (si_mask && !dump_mask)
+		return;
+
+	sys_info(dump_mask);
+}
-- 
2.53.0

[PATCH v2 2/4] watchdog: avoid sys_info fallback for all_bt

[Bradley Morgan]

The watchdog prints all CPU backtraces itself. When the watchdog mask
contains only SYS_INFO_ALL_BT, stripping that bit leaves zero and
sys_info(0) falls back to kernel_sys_info.

Use sys_info_without_all_bt() so an explicit all_bt mask does not request
the global default.

Fixes: a9af76a78760 ("watchdog: add sys_info sysctls to dump sys info on system lockup")
Cc: stable@vger.kernel.org
Signed-off-by: Bradley Morgan <include@grrlz.net>
---
Changes since v1:
- Use the shared sys_info_without_all_bt() helper.
- Keep the generic watchdog change separate from powerpc.

 kernel/watchdog.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 87dd5e0f6968..5bf24231a5d8 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -208,6 +208,7 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
 {
 	int hardlockup_all_cpu_backtrace;
 	unsigned int this_cpu;
+	unsigned long si_mask;
 	unsigned long flags;
 
 	if (per_cpu(watchdog_hardlockup_touched, cpu)) {
@@ -216,7 +217,8 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
 		return;
 	}
 
-	hardlockup_all_cpu_backtrace = (hardlockup_si_mask & SYS_INFO_ALL_BT) ?
+	si_mask = READ_ONCE(hardlockup_si_mask);
+	hardlockup_all_cpu_backtrace = (si_mask & SYS_INFO_ALL_BT) ?
 					1 : sysctl_hardlockup_all_cpu_backtrace;
 	/*
 	 * Check for a hardlockup by making sure the CPU's timer
@@ -286,7 +288,7 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
 			clear_bit_unlock(0, &hard_lockup_nmi_warn);
 	}
 
-	sys_info(hardlockup_si_mask & ~SYS_INFO_ALL_BT);
+	sys_info_without_all_bt(si_mask);
 	if (hardlockup_panic)
 		nmi_panic(regs, "Hard LOCKUP");
 
@@ -798,6 +800,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 	struct pt_regs *regs = get_irq_regs();
 	int softlockup_all_cpu_backtrace;
 	int duration, thresh_count;
+	unsigned long si_mask;
 	unsigned long flags;
 
 	if (!watchdog_enabled)
@@ -809,7 +812,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 	if (panic_in_progress())
 		return HRTIMER_NORESTART;
 
-	softlockup_all_cpu_backtrace = (softlockup_si_mask & SYS_INFO_ALL_BT) ?
+	si_mask = READ_ONCE(softlockup_si_mask);
+	softlockup_all_cpu_backtrace = (si_mask & SYS_INFO_ALL_BT) ?
 					1 : sysctl_softlockup_all_cpu_backtrace;
 
 	watchdog_hardlockup_kick();
@@ -900,7 +904,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 		}
 
 		add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
-		sys_info(softlockup_si_mask & ~SYS_INFO_ALL_BT);
+		sys_info_without_all_bt(si_mask);
 		thresh_count = duration / get_softlockup_thresh();
 
 		if (softlockup_panic && thresh_count >= softlockup_panic)
-- 
2.53.0

[PATCH v2 3/4] powerpc/watchdog: avoid sys_info fallback for all_bt

[Bradley Morgan]

The powerpc watchdog prints all CPU backtraces itself. When the watchdog
mask contains only SYS_INFO_ALL_BT, stripping that bit leaves zero and
sys_info(0) falls back to kernel_sys_info.

Use sys_info_without_all_bt() so an explicit all_bt mask does not request
the global default.

Fixes: e561383a39ed ("powerpc/watchdog: add support for hardlockup_sys_info sysctl")
Cc: stable@vger.kernel.org
Signed-off-by: Bradley Morgan <include@grrlz.net>
---
Changes since v1:
- Use the shared sys_info_without_all_bt() helper.
- Keep the powerpc watchdog change in its own patch.

 arch/powerpc/kernel/watchdog.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
index c40c69368476..813f9d48a6be 100644
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -201,6 +201,7 @@ static bool set_cpu_stuck(int cpu)
 static void watchdog_smp_panic(int cpu)
 {
 	static cpumask_t wd_smp_cpus_ipi; // protected by reporting
+	unsigned long si_mask;
 	unsigned long flags;
 	u64 tb, last_reset;
 	int c;
@@ -236,8 +237,9 @@ static void watchdog_smp_panic(int cpu)
 	pr_emerg("CPU %d TB:%lld, last SMP heartbeat TB:%lld (%lldms ago)\n",
 		 cpu, tb, last_reset, tb_to_ns(tb - last_reset) / 1000000);
 
+	si_mask = READ_ONCE(hardlockup_si_mask);
 	if (sysctl_hardlockup_all_cpu_backtrace ||
-	    (hardlockup_si_mask & SYS_INFO_ALL_BT)) {
+	    (si_mask & SYS_INFO_ALL_BT)) {
 		trigger_allbutcpu_cpu_backtrace(cpu);
 		cpumask_clear(&wd_smp_cpus_ipi);
 	} else {
@@ -251,7 +253,7 @@ static void watchdog_smp_panic(int cpu)
 		}
 	}
 
-	sys_info(hardlockup_si_mask & ~SYS_INFO_ALL_BT);
+	sys_info_without_all_bt(si_mask);
 	if (hardlockup_panic)
 		nmi_panic(NULL, "Hard LOCKUP");
 
@@ -371,6 +373,7 @@ static void watchdog_timer_interrupt(int cpu)
 
 DEFINE_INTERRUPT_HANDLER_NMI(soft_nmi_interrupt)
 {
+	unsigned long si_mask;
 	unsigned long flags;
 	int cpu = raw_smp_processor_id();
 	u64 tb;
@@ -418,11 +421,12 @@ DEFINE_INTERRUPT_HANDLER_NMI(soft_nmi_interrupt)
 
 		xchg(&__wd_nmi_output, 1); // see wd_lockup_ipi
 
+		si_mask = READ_ONCE(hardlockup_si_mask);
 		if (sysctl_hardlockup_all_cpu_backtrace ||
-		    (hardlockup_si_mask & SYS_INFO_ALL_BT))
+		    (si_mask & SYS_INFO_ALL_BT))
 			trigger_allbutcpu_cpu_backtrace(cpu);
 
-		sys_info(hardlockup_si_mask & ~SYS_INFO_ALL_BT);
+		sys_info_without_all_bt(si_mask);
 		if (hardlockup_panic)
 			nmi_panic(regs, "Hard LOCKUP");
 
-- 
2.53.0

[PATCH v2 4/4] panic: avoid duplicate all CPU backtraces from sys_info

[Bradley Morgan]

panic_other_cpus_shutdown() handles SYS_INFO_ALL_BT before stopping the
other CPUs. Do not ask sys_info() to handle that bit again later in the
panic path.

Use sys_info_without_all_bt() so panic_print=all_bt does not request more
output after the CPUs are stopped.

Fixes: b76e89e50fc3 ("panic: generalize panic_print's function to show sys info")
Cc: stable@vger.kernel.org
Signed-off-by: Bradley Morgan <include@grrlz.net>
---
Changes since v1:
- New patch using the same helper for panic.

 kernel/panic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/panic.c b/kernel/panic.c
index d030f88ad4ef..2cf229c7c0cf 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -683,7 +683,7 @@ void vpanic(const char *fmt, va_list args)
 	 */
 	atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
 
-	sys_info(panic_print);
+	sys_info_without_all_bt(panic_print);
 
 	kmsg_dump_desc(KMSG_DUMP_PANIC, buf);
 
-- 
2.53.0