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Message-ID: <20230731091754.1.I501ab68cb926ee33a7c87e063d207abf09b9943c@changeid>
Date: Mon, 31 Jul 2023 09:17:59 -0700
From: Douglas Anderson <dianders@...omium.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Petr Mladek <pmladek@...e.com>,
Douglas Anderson <dianders@...omium.org>,
kernel test robot <lkp@...el.com>,
Lecopzer Chen <lecopzer.chen@...iatek.com>,
Pingfan Liu <kernelfans@...il.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH] watchdog/hardlockup: Avoid large stack frames in watchdog_hardlockup_check()
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, let's declare
it as `static`. This has the downside of taking up 1K of memory all
the time on systems with `CONFIG_NR_CPUS` to 8192, but on systems with
smaller `CONFIG_NR_CPUS` it's not much emory (with 128 CPUs it's only
16 bytes of memory). Presumably anyone building a system with
`CONFIG_NR_CPUS=8192` can afford the extra 1K of memory.
NOTE: as part of this change, we no longer check the return value of
trigger_single_cpu_backtrace(). While we could do this and only call
cpumask_clear_cpu() if trigger_single_cpu_backtrace() didn't fail,
that's probably not worth it. There's no reason to believe that
trigger_cpumask_backtrace() will succeed at backtracing the CPU when
trigger_single_cpu_backtrace() failed.
Alternatives considered:
- Use kmalloc with GFP_ATOMIC to allocate. I decided against this
since relying on kmalloc when the system is hard locked up seems
like a bad idea.
- Change the arch_trigger_cpumask_backtrace() across all architectures
to take an extra parameter to get the needed behavior. This seems
like a lot of churn for a small savings.
Fixes: 77c12fc95980 ("watchdog/hardlockup: add a "cpu" param to watchdog_hardlockup_check()")
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/r/202307310955.pLZDhpnl-lkp@intel.com
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---
kernel/watchdog.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index be38276a365f..19db2357969a 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);
}
/*
@@ -178,8 +173,13 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
* hardlockups generating interleaving traces
*/
if (sysctl_hardlockup_all_cpu_backtrace &&
- !test_and_set_bit(0, &watchdog_hardlockup_all_cpu_dumped))
+ !test_and_set_bit(0, &watchdog_hardlockup_all_cpu_dumped)) {
+ static struct cpumask backtrace_mask;
+
+ cpumask_copy(&backtrace_mask, cpu_online_mask);
+ cpumask_clear_cpu(cpu, &backtrace_mask);
trigger_cpumask_backtrace(&backtrace_mask);
+ }
if (hardlockup_panic)
nmi_panic(regs, "Hard LOCKUP");
--
2.41.0.487.g6d72f3e995-goog
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