The patch titled pids: de_thread: don't clear session/pgrp pids for the old leader has been removed from the -mm tree. Its filename was pids-de_thread-dont-clear-session-pgrp-pids-for-the-old-leader.patch This patch was dropped because it was merged into mainline or a subsystem tree The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: pids: de_thread: don't clear session/pgrp pids for the old leader From: Oleg Nesterov <oleg@xxxxxxxxxx> 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@xxxxxxxxxx> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Cc: Pavel Emelyanov <xemul@xxxxxxxxxx> Cc: Roland McGrath <roland@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/pid.c | 1 - 1 file changed, 1 deletion(-) diff -puN kernel/pid.c~pids-de_thread-dont-clear-session-pgrp-pids-for-the-old-leader kernel/pid.c --- a/kernel/pid.c~pids-de_thread-dont-clear-session-pgrp-pids-for-the-old-leader +++ a/kernel/pid.c @@ -354,7 +354,6 @@ void transfer_pid(struct task_struct *ol { 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) _ Patches currently in -mm which might be from oleg@xxxxxxxxxx are origin.patch posix-timers-bug-10460-discard-the-pending-signal-when-the-timer-is-destroyed.patch workqueue-remove-redundant-function-invocation.patch put_pid-make-sure-we-dont-free-the-live-pid.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html