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Commit 0f736a52 authored by Tetsuo Handa's avatar Tetsuo Handa Committed by Ingo Molnar
Browse files

locking/lockdep: Use for_each_process_thread() for debug_show_all_locks() 



debug_show_all_locks() tries to grab the tasklist_lock for two seconds, but
calling while_each_thread() without tasklist_lock held is not safe.

See the following commit for more information:

  4449a51a ("vm_is_stack: use for_each_thread() rather then buggy while_each_thread()")

Change debug_show_all_locks() from "do_each_thread()/while_each_thread()
with possibility of missing tasklist_lock" to "for_each_process_thread()
with RCU", and add a call to touch_all_softlockup_watchdogs() like
show_state_filter() does.

Signed-off-by: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1523011279-8206-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 12e2c411

kernel/locking/lockdep.c

+8 −35
Original line number Diff line number Diff line
@@ -4451,8 +4451,6 @@ EXPORT_SYMBOL_GPL(debug_check_no_locks_held); 
void debug_show_all_locks(void)

{

	struct task_struct *g, *p;

	int count = 10;

	int unlock = 1;



	if (unlikely(!debug_locks)) {

		pr_warn("INFO: lockdep is turned off.\n");
@@ -4460,30 +4458,8 @@ void debug_show_all_locks(void) 
	}

	pr_warn("\nShowing all locks held in the system:\n");



	/*

	 * Here we try to get the tasklist_lock as hard as possible,

	 * if not successful after 2 seconds we ignore it (but keep

	 * trying). This is to enable a debug printout even if a

	 * tasklist_lock-holding task deadlocks or crashes.

	 */

retry:

	if (!read_trylock(&tasklist_lock)) {

		if (count == 10)

			pr_warn("hm, tasklist_lock locked, retrying... ");

		if (count) {

			count--;

			pr_cont(" #%d", 10-count);

			mdelay(200);

			goto retry;

		}

		pr_cont(" ignoring it.\n");

		unlock = 0;

	} else {

		if (count != 10)

			pr_cont(" locked it.\n");

	}



	do_each_thread(g, p) {

	rcu_read_lock();

	for_each_process_thread(g, p) {

		/*

		 * It's not reliable to print a task's held locks

		 * if it's not sleeping (or if it's not the current
@@ -4491,19 +4467,16 @@ void debug_show_all_locks(void) 
		 */

		if (p->state == TASK_RUNNING && p != current)

			continue;

		if (p->lockdep_depth)

		if (!p->lockdep_depth)

			continue;

		lockdep_print_held_locks(p);

		if (!unlock)

			if (read_trylock(&tasklist_lock))

				unlock = 1;

		touch_nmi_watchdog();

	} while_each_thread(g, p);

		touch_all_softlockup_watchdogs();

	}

	rcu_read_unlock();



	pr_warn("\n");

	pr_warn("=============================================\n\n");



	if (unlock)

		read_unlock(&tasklist_lock);

}

EXPORT_SYMBOL_GPL(debug_show_all_locks);

#endif