17 Jul, 2009
3 commits
-
is_current_single_threaded() can safely miss a freshly forked CLONE_VM
task, but in this case it must not miss its parent. That is why we take
mm->mmap_sem for writing to make sure a thread/task with the same ->mm
can't pass exit_mm() and disappear.However we can avoid ->mmap_sem and rely on rcu/barriers:
- if we do not see the exiting parent on thread/process list
we see the result of list_del_rcu(), in this case we must
also see the result of list_add_rcu() which does wmb().- if we do see the parent but its ->mm == NULL, we need rmb()
to make sure we can't miss the child.Signed-off-by: Oleg Nesterov
Acked-by: David Howells
Signed-off-by: James Morris -
- is_single_threaded(task) is not safe unless task == current,
we can't use task->signal or task->mm.- it doesn't make sense unless task == current, the task can
fork right after the check.Rename it to current_is_single_threaded() and kill the argument.
Signed-off-by: Oleg Nesterov
Acked-by: David Howells
Signed-off-by: James Morris -
- Fix the comment, is_single_threaded(p) actually means that nobody shares
->mm with p.I think this helper should be renamed, and it should not have arguments.
With or without this patch it must not be used unless p == current,
otherwise we can't safely use p->signal or p->mm.- "if (atomic_read(&p->signal->count) != 1)" is not right when we have a
zombie group leader, use signal->live instead.- Add PF_KTHREAD check to skip kernel threads which may borrow p->mm,
otherwise we can return the wrong "false".- Use for_each_process() instead of do_each_thread(), all threads must use
the same ->mm.- Use down_write(mm->mmap_sem) + rcu_read_lock() instead of tasklist_lock
to iterate over the process list. If there is another CLONE_VM process
it can't pass exit_mm() which takes the same mm->mmap_sem. We can miss
a freshly forked CLONE_VM task, but this doesn't matter because we must
see its parent and return false.Signed-off-by: Oleg Nesterov
Cc: David Howells
Cc: James Morris
Cc: Roland McGrath
Cc: Stephen Smalley
Signed-off-by: Andrew Morton
Signed-off-by: James Morris
14 Nov, 2008
1 commit
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Rename is_single_threaded() to is_wq_single_threaded() so that a new
is_single_threaded() can be created that refers to tasks rather than
waitqueues.Signed-off-by: David Howells
Reviewed-by: James Morris
Signed-off-by: James Morris
