[PATCH 3/3] coredump: zap_threads() must skip kernel threads

[Oleg Nesterov]

The main loop in zap_threads() must skip kthreads which may use the same mm.
Otherwise we "kill" this thread erroneously (for example, it can not fork or
exec after that), and the coredumping task stucks in the TASK_UNINTERRUPTIBLE
state forever because of the wrong ->core_waiters count.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>

--- 26-rc2/fs/exec.c~3_CD_FIX_RACE_USE_MM	2008-05-31 20:05:21.000000000 +0400
+++ 26-rc2/fs/exec.c	2008-06-01 19:04:39.000000000 +0400
@@ -1568,11 +1568,13 @@ static inline int zap_threads(struct tas
 	for_each_process(g) {
 		if (g == tsk->group_leader)
 			continue;
+		if (g->flags & PF_KTHREAD)
+			continue;
 
 		p = g;
 		do {
 			if (p->mm) {
-				if (p->mm == mm) {
+				if (unlikely(p->mm == mm)) {
 					lock_task_sighand(p, &flags);
 					zap_process(p);
 					unlock_task_sighand(p, &flags);

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