linux-kernel - [tip:locking/urgent] locking/lockdep: Avoid triggering hardlockup from debug_show_all

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Date:   Wed, 24 Jan 2018 02:38:22 -0800
From:   tip-bot for Tejun Heo <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, hpa@...or.com, peterz@...radead.org,
        mingo@...nel.org, tj@...nel.org, torvalds@...ux-foundation.org,
        tglx@...utronix.de
Subject: [tip:locking/urgent] locking/lockdep: Avoid triggering hardlockup
 from debug_show_all_locks()

Commit-ID:  88f1c87de11a86d839f4ce5313e552d96709b990
Gitweb:     https://git.kernel.org/tip/88f1c87de11a86d839f4ce5313e552d96709b990
Author:     Tejun Heo <tj@...nel.org>
AuthorDate: Mon, 22 Jan 2018 14:00:55 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 24 Jan 2018 10:00:09 +0100

locking/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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: kernel-team@...com
Link: http://lkml.kernel.org/r/20180122220055.GB1771050@devbig577.frc2.facebook.com
Signed-off-by: Ingo Molnar <mingo@...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 @@ retry:
 		if (!unlock)
 			if (read_trylock(&tasklist_lock))
 				unlock = 1;
+		touch_nmi_watchdog();
 	} while_each_thread(g, p);
 
 	pr_warn("\n");