Messages in this thread Patch in this message | | | From | Douglas Anderson <> | Subject | [PATCH] watchdog/hardlockup: Avoid large stack frames in watchdog_hardlockup_check() | Date | Mon, 31 Jul 2023 09:17:59 -0700 |
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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@intel.com> Closes: https://lore.kernel.org/r/202307310955.pLZDhpnl-lkp@intel.com Signed-off-by: Douglas Anderson <dianders@chromium.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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