[PATCH v3 2/2] watchdog/hardlockup: Avoid large stack frames in watchdog_hardlockup_check()

From: Douglas Anderson
Date: Thu Aug 03 2023 - 19:09:05 EST


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.

We'll use the new trigger_allbutcpu_cpu_backtrace() to avoid needing
to use a CPU mask at all.

Fixes: 77c12fc95980 ("watchdog/hardlockup: add a "cpu" param to watchdog_hardlockup_check()")
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/r/202307310955.pLZDhpnl-lkp@xxxxxxxxx
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---

Changes in v3:
- Rebase on change introducing trigger_allbutcpu_cpu_backtrace().

Changes in v2:
- Allocate space when userspace requests all cpus be backtraced.

kernel/watchdog.c | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 085d7a78f62f..d145305d95fe 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -151,9 +151,6 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
*/
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))
@@ -167,10 +164,8 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
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);
}

/*
@@ -179,7 +174,7 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
*/
if (sysctl_hardlockup_all_cpu_backtrace &&
!test_and_set_bit(0, &watchdog_hardlockup_all_cpu_dumped))
- trigger_cpumask_backtrace(&backtrace_mask);
+ trigger_allbutcpu_cpu_backtrace(cpu);

if (hardlockup_panic)
nmi_panic(regs, "Hard LOCKUP");
--
2.41.0.585.gd2178a4bd4-goog