linux-kernel - [PATCH] lockdep: Avoid triggering hardlockup from debug_show_all

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Message-ID: <20180122220055.GB1771050@devbig577.frc2.facebook.com>
Date:   Mon, 22 Jan 2018 14:00:55 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com
Subject: [PATCH] lockdep: Avoid triggering hardlockup from
 debug_show_all_locks()

debug_show_all_locks() iterates all tasks and print held locks whole
holding tasklist_lock.  This can take a while on a slow console device
and may end up triggering NMI hardlockup detector if someone else ends
up waiting for tasklist_lock.

Touch the NMI watchdog while printing the held locks to avoid
spuriously triggering the hardlockup detector.

Signed-off-by: Tejun Heo <tj@...nel.org>
---
 kernel/locking/lockdep.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 5fa1324..5216590 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -49,6 +49,7 @@
 #include <linux/gfp.h>
 #include <linux/random.h>
 #include <linux/jhash.h>
+#include <linux/nmi.h>
 
 #include <asm/sections.h>
 
@@ -4490,6 +4491,7 @@ void debug_show_all_locks(void)
 		if (!unlock)
 			if (read_trylock(&tasklist_lock))
 				unlock = 1;
+		touch_nmi_watchdog();
 	} while_each_thread(g, p);
 
 	pr_warn("\n");