[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@xxxxxxxxxxxxxxx
Signed-off-by: Bradley Morgan <include@xxxxxxxxx>
---
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