linux-kernel - [PATCH 3.16 125/125] vm_is_stack: use for_each_thread() rather then buggy while_each

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Date:	Wed,  3 Sep 2014 15:08:02 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Aleksei Besogonov <alex.besogonov@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 3.16 125/125] vm_is_stack: use for_each_thread() rather then buggy while_each_thread()

3.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Oleg Nesterov <oleg@...hat.com>

commit 4449a51a7c281602d3a385044ab928322a122a02 upstream.

Aleksei hit the soft lockup during reading /proc/PID/smaps.  David
investigated the problem and suggested the right fix.

while_each_thread() is racy and should die, this patch updates
vm_is_stack().

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Reported-by: Aleksei Besogonov <alex.besogonov@...il.com>
Tested-by: Aleksei Besogonov <alex.besogonov@...il.com>
Suggested-by: David Rientjes <rientjes@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/util.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- a/mm/util.c
+++ b/mm/util.c
@@ -277,17 +277,14 @@ pid_t vm_is_stack(struct task_struct *ta
 
 	if (in_group) {
 		struct task_struct *t;
-		rcu_read_lock();
-		if (!pid_alive(task))
-			goto done;
 
-		t = task;
-		do {
+		rcu_read_lock();
+		for_each_thread(task, t) {
 			if (vm_is_stack_for_task(t, vma)) {
 				ret = t->pid;
 				goto done;
 			}
-		} while_each_thread(task, t);
+		}
 done:
 		rcu_read_unlock();
 	}


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