The patch titled
Subject: watchdog/hardlockup: avoid large stack frames in watchdog_hardlockup_check()
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
watchdog-hardlockup-avoid-large-stack-frames-in-watchdog_hardlockup_check.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/watchdog-hardlockup-avoid-large-stack-frames-in-watchdog_hardlockup_check.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Douglas Anderson <dianders@xxxxxxxxxxxx>
Subject: watchdog/hardlockup: avoid large stack frames in watchdog_hardlockup_check()
Date: Wed, 2 Aug 2023 12:26:00 -0700
After commit 77c12fc95980 ("watchdog/hardlockup: add a "cpu" param to
watchdog_hardlockup_check()") we started storing a `struct cpumask` on the
stack in watchdog_hardlockup_check(). On systems with CONFIG_NR_CPUS set
to 8192 this takes up 1K on the stack. That triggers warnings with
`CONFIG_FRAME_WARN` set to 1024.
Instead of putting this `struct cpumask` on the stack, we'll allocate it
on the heap whenever userspace tells us that they want to backtrace all
CPUs upon a hardlockup.
NOTE: the reason that this mask is even needed is to make sure that we can
print the hung CPU first, which makes the logs much easier to understand.
Link: https://lkml.kernel.org/r/20230802122555.v2.1.I501ab68cb926ee33a7c87e063d207abf09b9943c@changeid
Fixes: 77c12fc95980 ("watchdog/hardlockup: add a "cpu" param to watchdog_hardlockup_check()")
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/r/202307310955.pLZDhpnl-lkp@xxxxxxxxx
Cc: Lecopzer Chen <lecopzer.chen@xxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Pingfan Liu <kernelfans@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/watchdog.c | 44 ++++++++++++++++++++++++++++++++++----------
1 file changed, 34 insertions(+), 10 deletions(-)
--- a/kernel/watchdog.c~watchdog-hardlockup-avoid-large-stack-frames-in-watchdog_hardlockup_check
+++ a/kernel/watchdog.c
@@ -93,6 +93,8 @@ static DEFINE_PER_CPU(bool, watchdog_har
static DEFINE_PER_CPU(bool, watchdog_hardlockup_touched);
static unsigned long watchdog_hardlockup_all_cpu_dumped;
+static struct cpumask *hardlockup_backtrace_mask;
+
notrace void arch_touch_nmi_watchdog(void)
{
/*
@@ -106,6 +108,29 @@ notrace void arch_touch_nmi_watchdog(voi
}
EXPORT_SYMBOL(arch_touch_nmi_watchdog);
+static int hardlockup_all_cpu_backtrace_proc_handler(struct ctl_table *table, int write,
+ void *buffer, size_t *lenp, loff_t *ppos)
+{
+ int ret;
+
+ ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+
+ /*
+ * Only allocate memory for the backtrace mask if userspace actually
+ * wants to trace all CPUs since this can take up 1K of space on a
+ * system with CONFIG_NR_CPUS=8192.
+ */
+ if (sysctl_hardlockup_all_cpu_backtrace && !hardlockup_backtrace_mask) {
+ hardlockup_backtrace_mask =
+ kzalloc(sizeof(*hardlockup_backtrace_mask), GFP_KERNEL);
+ } else if (!sysctl_hardlockup_all_cpu_backtrace && hardlockup_backtrace_mask) {
+ kfree(hardlockup_backtrace_mask);
+ hardlockup_backtrace_mask = NULL;
+ }
+
+ return ret;
+}
+
void watchdog_hardlockup_touch_cpu(unsigned int cpu)
{
per_cpu(watchdog_hardlockup_touched, cpu) = true;
@@ -151,9 +176,6 @@ void watchdog_hardlockup_check(unsigned
*/
if (is_hardlockup(cpu)) {
unsigned int this_cpu = smp_processor_id();
- struct cpumask backtrace_mask;
-
- cpumask_copy(&backtrace_mask, cpu_online_mask);
/* Only print hardlockups once. */
if (per_cpu(watchdog_hardlockup_warned, cpu))
@@ -167,19 +189,20 @@ void watchdog_hardlockup_check(unsigned
show_regs(regs);
else
dump_stack();
- cpumask_clear_cpu(cpu, &backtrace_mask);
} else {
- if (trigger_single_cpu_backtrace(cpu))
- cpumask_clear_cpu(cpu, &backtrace_mask);
+ trigger_single_cpu_backtrace(cpu);
}
/*
* Perform multi-CPU dump only once to avoid multiple
* hardlockups generating interleaving traces
*/
- if (sysctl_hardlockup_all_cpu_backtrace &&
- !test_and_set_bit(0, &watchdog_hardlockup_all_cpu_dumped))
- trigger_cpumask_backtrace(&backtrace_mask);
+ if (hardlockup_backtrace_mask &&
+ !test_and_set_bit(0, &watchdog_hardlockup_all_cpu_dumped)) {
+ cpumask_copy(hardlockup_backtrace_mask, cpu_online_mask);
+ cpumask_clear_cpu(cpu, hardlockup_backtrace_mask);
+ trigger_cpumask_backtrace(hardlockup_backtrace_mask);
+ }
if (hardlockup_panic)
nmi_panic(regs, "Hard LOCKUP");
@@ -192,6 +215,7 @@ void watchdog_hardlockup_check(unsigned
#else /* CONFIG_HARDLOCKUP_DETECTOR_COUNTS_HRTIMER */
+#define hardlockup_all_cpu_backtrace_proc_handler proc_dointvec_minmax
static inline void watchdog_hardlockup_kick(void) { }
#endif /* !CONFIG_HARDLOCKUP_DETECTOR_COUNTS_HRTIMER */
@@ -916,7 +940,7 @@ static struct ctl_table watchdog_sysctls
.data = &sysctl_hardlockup_all_cpu_backtrace,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec_minmax,
+ .proc_handler = hardlockup_all_cpu_backtrace_proc_handler,
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE,
},
_
Patches currently in -mm which might be from dianders@xxxxxxxxxxxx are
watchdog-hardlockup-avoid-large-stack-frames-in-watchdog_hardlockup_check.patch
