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Date: Tue, 29 Jan 2008 19:40:19 +0300 From: Oleg Nesterov <oleg@...sign.ru> To: Andrew Morton <akpm@...ux-foundation.org> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, Ingo Molnar <mingo@...e.hu>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Pavel Emelyanov <xemul@...nvz.org>, linux-kernel@...r.kernel.org Subject: [PATCH] fix tasklist + find_pid() with CONFIG_PREEMPT_RCU With CONFIG_PREEMPT_RCU read_lock(tasklist_lock) doesn't imply rcu_read_lock(), but find_pid_ns()->hlist_for_each_entry_rcu() should be safe under tasklist. Usually it is, detach_pid() is always called under write_lock(tasklist_lock), but copy_process() calls free_pid() lockless. "#ifdef CONFIG_PREEMPT_RCU" is added mostly as documentation, perhaps it is too ugly and should be removed. Signed-off-by: Oleg Nesterov <oleg@...sign.ru> --- MM/kernel/fork.c~PR_RCU 2008-01-27 17:09:47.000000000 +0300 +++ MM/kernel/fork.c 2008-01-29 19:23:44.000000000 +0300 @@ -1335,8 +1335,19 @@ static struct task_struct *copy_process( return p; bad_fork_free_pid: - if (pid != &init_struct_pid) + if (pid != &init_struct_pid) { +#ifdef CONFIG_PREEMPT_RCU + /* + * read_lock(tasklist_lock) doesn't imply rcu_read_lock(), + * make sure find_pid() is safe under read_lock(tasklist). + */ + write_lock_irq(&tasklist_lock); +#endif free_pid(pid); +#ifdef CONFIG_PREEMPT_RCU + write_unlock_irq(&tasklist_lock); +#endif + } bad_fork_cleanup_namespaces: exit_task_namespaces(p); bad_fork_cleanup_keys: -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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