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authorOleg Nesterov <oleg@tv-sign.ru>2008-04-30 00:54:25 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-30 08:29:48 -0700
commit65450cebc6a2efde80ed45514f727e6e4dc1eafd (patch)
tree26d3cdb75b4e94eed773c71c4bcb3c5d5843eed3
parent5cd204550b1a006f2b0c986b0e0f53220ebfd391 (diff)
pids: de_thread: don't clear session/pgrp pids for the old leader
Based on Eric W. Biederman's idea. Unless task == current, without tasklist_lock held task_session()/task_pgrp() can return NULL if the caller races with de_thread() which switches the group leader. Change transfer_pid() to not clear old->pids[type].pid for the old leader. This means that its .pid can point to "nowhere", but this is already true for sub-threads, and the old leader is not group_leader() any longer. IOW, with or without this change we can't trust task's special pids unless it is the group leader. With this change the following code rcu_read_lock(); task = find_task_by_xxx(); do_something(task_pgrp(task), task_session(task)); rcu_read_unlock(); can't race with exec and hit the NULL pid. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Pavel Emelyanov <xemul@openvz.org> Cc: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--kernel/pid.c1
1 files changed, 0 insertions, 1 deletions
diff --git a/kernel/pid.c b/kernel/pid.c
index a9ae9f7fb22..e9a31d362b2 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -354,7 +354,6 @@ void transfer_pid(struct task_struct *old, struct task_struct *new,
{
new->pids[type].pid = old->pids[type].pid;
hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
- old->pids[type].pid = NULL;
}
struct task_struct *pid_task(struct pid *pid, enum pid_type type)