Re: [PATCH] ftrace: do_each_pid_task() needs rcu lock

[Eric W. Biederman]

Oleg Nesterov <oleg@xxxxxxxxxx> writes:

> On 02/03, Oleg Nesterov wrote:
>>
>> "ftrace: use struct pid" commit 978f3a45d9499c7a447ca7615455cefb63d44165
>> converted ftrace_pid_trace to "struct pid*". But we can't use
>> do_each_pid_task() without rcu_read_lock() even if we know the pid
>> itself can't go away (it was pinned in ftrace_pid_write). The exiting
>> task can detach itself from this pid at any moment.
>
> Q: why do we use do_each_pid_task(PIDTYPE_PID) ? We can never have more
> than 1 task in the loop. Perhaps,

That is a bug in do_each_pid_task(PIDTYPE_PID).
For ftrace we really want to grab all tasks with a given pid even
in the crazy exec case.

Eric
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/