Commit c7e49c14 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

ptrace: optimize exit_ptrace() for the likely case 



exit_ptrace() takes tasklist_lock unconditionally.  We need this lock to
avoid the race with ptrace_traceme(), it acts as a barrier.

Change its caller, forget_original_parent(), to call exit_ptrace() under
tasklist_lock.  Change exit_ptrace() to drop and reacquire this lock if
needed.

This allows us to add the fastpath list_empty(ptraced) check.  In the
likely no-tracees case exit_ptrace() just returns and we avoid the lock()
+ unlock() sequence.

"Zhang, Yanmin" <yanmin_zhang@linux.intel.com> suggested to add this
check, and he reports that this change adds about 11% improvement in some
tests.

Suggested-and-tested-by: default avatar"Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarRoland McGrath <roland@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 13d7e3a2

kernel/exit.c

+5 −2
Original line number Diff line number Diff line
@@ -771,9 +771,12 @@ static void forget_original_parent(struct task_struct *father) 
	struct task_struct *p, *n, *reaper;

	LIST_HEAD(dead_children);



	exit_ptrace(father);



	write_lock_irq(&tasklist_lock);

	/*

	 * Note that exit_ptrace() and find_new_reaper() might

	 * drop tasklist_lock and reacquire it.

	 */

	exit_ptrace(father);

	reaper = find_new_reaper(father);



	list_for_each_entry_safe(p, n, &father->children, sibling) {

kernel/ptrace.c

+9 −3
Original line number Diff line number Diff line
@@ -324,26 +324,32 @@ int ptrace_detach(struct task_struct *child, unsigned int data) 
}



/*

 * Detach all tasks we were using ptrace on.

 * Detach all tasks we were using ptrace on. Called with tasklist held

 * for writing, and returns with it held too. But note it can release

 * and reacquire the lock.

 */

void exit_ptrace(struct task_struct *tracer)

{

	struct task_struct *p, *n;

	LIST_HEAD(ptrace_dead);



	write_lock_irq(&tasklist_lock);

	if (likely(list_empty(&tracer->ptraced)))

		return;



	list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) {

		if (__ptrace_detach(tracer, p))

			list_add(&p->ptrace_entry, &ptrace_dead);

	}

	write_unlock_irq(&tasklist_lock);



	write_unlock_irq(&tasklist_lock);

	BUG_ON(!list_empty(&tracer->ptraced));



	list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_entry) {

		list_del_init(&p->ptrace_entry);

		release_task(p);

	}



	write_lock_irq(&tasklist_lock);

}



int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)

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