user/sven/linux.git/kernel/exit.c, branch v2.6.35.4

proc: turn signal_struct->count into "int nr_threads"

2010-05-27T16:12:47Z

No functional changes, just s/atomic_t count/int nr_threads/. With the recent changes this counter has a single user, get_nr_threads() And, none of its callers need the really accurate number of threads, not to mention each caller obviously races with fork/exit. It is only used to report this value to the user-space, except first_tid() uses it to avoid the unnecessary while_each_thread() loop in the unlikely case. It is a bit sad we need a word in struct signal_struct for this, perhaps we can change get_nr_threads() to approximate the number of threads using signal->live and kill ->nr_threads later. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Oleg Nesterov Cc: Alexey Dobriyan Cc: "Eric W. Biederman" Acked-by: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

exit: move taskstats_tgid_free() from __exit_signal() to free_signal_struct()

2010-05-27T16:12:46Z

Move taskstats_tgid_free() from __exit_signal() to free_signal_struct(). This way signal->stats never points to nowhere and we can read ->stats lockless. Signed-off-by: Oleg Nesterov Cc: Balbir Singh Cc: Roland McGrath Cc: Veaceslav Falico Cc: Stanislaw Gruszka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

exit: __exit_signal: use thread_group_leader() consistently

2010-05-27T16:12:46Z

Cleanup: - Add the boolean, group_dead = thread_group_leader(), for clarity. - Do not test/set sig == NULL to detect the all-dead case, use this boolean. - Pass this boolen to __unhash_process() and use it instead of another thread_group_leader() call which needs ->group_leader. This can be considered as microoptimization, but hopefully this also allows us do do other cleanups later. Signed-off-by: Oleg Nesterov Cc: Balbir Singh Cc: Roland McGrath Cc: Veaceslav Falico Cc: Stanislaw Gruszka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

signals: kill the awful task_rq_unlock_wait() hack

2010-05-27T16:12:46Z

Now that task->signal can't go away we can revert the horrible hack added by ad474caca3e2a0550b7ce0706527ad5ab389a4d4 ("fix for account_group_exec_runtime(), make sure ->signal can't be freed under rq->lock"). And we can do more cleanups sched_stats.h/posix-cpu-timers.c later. Signed-off-by: Oleg Nesterov Cc: Alan Cox Cc: Ingo Molnar Cc: Peter Zijlstra Acked-by: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

signals: clear signal->tty when the last thread exits

2010-05-27T16:12:46Z

When the last thread exits signal->tty is freed, but the pointer is not cleared and points to nowhere. This is OK. Nobody should use signal->tty lockless, and it is no longer possible to take ->siglock. However this looks wrong even if correct, and the nice OOPS is better than subtle and hard to find bugs. Change __exit_signal() to clear signal->tty under ->siglock. Note: __exit_signal() needs more cleanups. It should not check "sig != NULL" to detect the all-dead case and we have the same issues with signal->stats. Signed-off-by: Oleg Nesterov Cc: Alan Cox Cc: Ingo Molnar Acked-by: Peter Zijlstra Acked-by: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

signals: make task_struct->signal immutable/refcountable

2010-05-27T16:12:46Z

We have a lot of problems with accessing task_struct->signal, it can "disappear" at any moment. Even current can't use its ->signal safely after exit_notify(). ->siglock helps, but it is not convenient, not always possible, and sometimes it makes sense to use task->signal even after this task has already dead. This patch adds the reference counter, sigcnt, into signal_struct. This reference is owned by task_struct and it is dropped in __put_task_struct(). Perhaps it makes sense to export get/put_signal_struct() later, but currently I don't see the immediate reason. Rename __cleanup_signal() to free_signal_struct() and unexport it. With the previous changes it does nothing except kmem_cache_free(). Change __exit_signal() to not clear/free ->signal, it will be freed when the last reference to any thread in the thread group goes away. Note: - when the last thead exits signal->tty can point to nowhere, see the next patch. - with or without this patch signal_struct->count should go away, or at least it should be "int nr_threads" for fs/proc. This will be addressed later. Signed-off-by: Oleg Nesterov Cc: Alan Cox Cc: Ingo Molnar Cc: Peter Zijlstra Acked-by: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

fork/exit: move tty_kref_put() outside of __cleanup_signal()

2010-05-27T16:12:46Z

tty_kref_put() has two callsites in copy_process() paths, 1. if copy_process() suceeds it is called before we copy signal->tty from parent 2. otherwise it is called from __cleanup_signal() under bad_fork_cleanup_signal: label In both cases tty_kref_put() is not right and unneeded because we don't have the balancing tty_kref_get(). Fortunately, this is harmless because this can only happen without CLONE_THREAD, and in this case signal->tty must be NULL. Remove tty_kref_put() from copy_process() and __cleanup_signal(), and change another caller of __cleanup_signal(), __exit_signal(), to call tty_kref_put() by hand. I hope this change makes sense by itself, but it is also needed to make ->signal refcountable. Signed-off-by: Oleg Nesterov Acked-by: Alan Cox Acked-by: Roland McGrath Cc: Greg KH Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

exit: avoid sig->count in __exit_signal() to detect the group-dead case

2010-05-27T16:12:46Z

Change __exit_signal() to check thread_group_leader() instead of atomic_dec_and_test(&sig->count). This must be equivalent, the group leader must be released only after all other threads have exited and passed __exit_signal(). Henceforth sig->count is not actually used, except in fs/proc for get_nr_threads/etc. Signed-off-by: Oleg Nesterov Acked-by: Roland McGrath Cc: Veaceslav Falico Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

exit: avoid sig->count in de_thread/__exit_signal synchronization

2010-05-27T16:12:46Z

de_thread() and __exit_signal() use signal_struct->count/notify_count for synchronization. We can simplify the code and use ->notify_count only. Instead of comparing these two counters, we can change de_thread() to set ->notify_count = nr_of_sub_threads, then change __exit_signal() to dec-and-test this counter and notify group_exit_task. Note that __exit_signal() checks "notify_count > 0" just for symmetry with exit_notify(), we could just check it is != 0. Signed-off-by: Oleg Nesterov Acked-by: Roland McGrath Cc: Veaceslav Falico Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

exit: exit_notify() can trust signal->notify_count < 0

2010-05-27T16:12:45Z

signal_struct->count in its current form must die. - it has no reasons to be atomic_t - it looks like a reference counter, but it is not - otoh, we really need to make task->signal refcountable, just look at the extremely ugly task_rq_unlock_wait() called from __exit_signals(). - we should change the lifetime rules for task->signal, it should be pinned to task_struct. We have a lot of code which can be simplified after that. - it is not needed! while the code is correct, any usage of this counter is artificial, except fs/proc uses it correctly to show the number of threads. This series removes the usage of sig->count from exit pathes. This patch: Now that Veaceslav changed copy_signal() to use zalloc(), exit_notify() can just check notify_count < 0 to ensure the execing sub-threads needs the notification from us. No need to do other checks, notify_count != 0 must always mean ->group_exit_task != NULL is waiting for us. Signed-off-by: Oleg Nesterov Acked-by: Roland McGrath Cc: Veaceslav Falico Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds