watchdog: softlockup: panic when lockup duration exceeds N thresholds

The softlockup_panic sysctl is currently a binary option: panic
immediately or never panic on soft lockups.

Panicking on any soft lockup, regardless of duration, can be overly
aggressive for brief stalls that may be caused by legitimate operations. 
Conversely, never panicking may allow severe system hangs to persist
undetected.

Extend softlockup_panic to accept an integer threshold, allowing the
kernel to panic only when the normalized lockup duration exceeds N
watchdog threshold periods.  This provides finer-grained control to
distinguish between transient delays and persistent system failures.

The accepted values are:
- 0: Don't panic (unchanged)
- 1: Panic when duration >= 1 * threshold (20s default, original behavior)
- N > 1: Panic when duration >= N * threshold (e.g., 2 = 40s, 3 = 60s.)

The original behavior is preserved for values 0 and 1, maintaining full
backward compatibility while allowing systems to tolerate brief lockups
while still catching severe, persistent hangs.

[lirongqing@baidu.com: v2]
  Link: https://lkml.kernel.org/r/20251218074300.4080-1-lirongqing@baidu.com
Link: https://lkml.kernel.org/r/20251216074521.2796-1-lirongqing@baidu.com
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Hao Luo <haoluo@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Song Liu <song@kernel.org>
Cc: Stanislav Fomichev <sdf@fomichev.me>
Cc: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 7 insertions, 5 deletions

diff --git a/kernel/configs/debug.config b/kernel/configs/debug.config
index 9f6ab7dabf67..774702591d26 100644
--- a/kernel/configs/debug.config
+++ b/kernel/configs/debug.config
@@ -84,7 +84,7 @@ CONFIG_SLUB_DEBUG_ON=y
 # Debug Oops, Lockups and Hangs
 #
 CONFIG_BOOTPARAM_HUNG_TASK_PANIC=0
-# CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC is not set
+CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC=0
 CONFIG_DEBUG_ATOMIC_SLEEP=y
 CONFIG_DETECT_HUNG_TASK=y
 CONFIG_PANIC_ON_OOPS=y
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 366122f4a0f8..b4d5fbdb933a 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -363,7 +363,7 @@ static struct cpumask watchdog_allowed_mask __read_mostly;
 
 /* Global variables, exported for sysctl */
 unsigned int __read_mostly softlockup_panic =
-			IS_ENABLED(CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC);
+			CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC;
 
 static bool softlockup_initialized __read_mostly;
 static u64 __read_mostly sample_period;
@@ -774,8 +774,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 {
 	unsigned long touch_ts, period_ts, now;
 	struct pt_regs *regs = get_irq_regs();
-	int duration;
 	int softlockup_all_cpu_backtrace;
+	int duration, thresh_count;
 	unsigned long flags;
 
 	if (!watchdog_enabled)
@@ -879,7 +879,9 @@ 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);
-		if (softlockup_panic)
+		thresh_count = duration / get_softlockup_thresh();
+
+		if (softlockup_panic && thresh_count >= softlockup_panic)
 			panic("softlockup: hung tasks");
 	}
 
@@ -1228,7 +1230,7 @@ static const struct ctl_table watchdog_sysctls[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_ONE,
+		.extra2		= SYSCTL_INT_MAX,
 	},
 	{
 		.procname	= "softlockup_sys_info",