Patch "watchdog/hardlockup: avoid large stack frames in watchdog_hardlockup_check()" has been added to the 6.5-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    watchdog/hardlockup: avoid large stack frames in watchdog_hardlockup_check()

to the 6.5-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     watchdog-hardlockup-avoid-large-stack-frames-in-watc.patch
and it can be found in the queue-6.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ee2523775476f30621b234fb53ad1110b2d0e9a2
Author: Douglas Anderson <dianders@xxxxxxxxxxxx>
Date:   Fri Aug 4 07:00:43 2023 -0700

    watchdog/hardlockup: avoid large stack frames in watchdog_hardlockup_check()
    
    [ Upstream commit 1f38c86bb29f4548b8df01b47a313518e6ed2dfe ]
    
    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.
    
    Link: https://lkml.kernel.org/r/20230804065935.v4.2.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
    Acked-by: Michal Hocko <mhocko@xxxxxxxx>
    Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
    Cc: Lecopzer Chen <lecopzer.chen@xxxxxxxxxxxx>
    Cc: Pingfan Liu <kernelfans@xxxxxxxxx>
    Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 085d7a78f62f0..d145305d95fe8 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");