From: Oleg Nesterov <oleg@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>,
gregkh@linuxfoundation.org, jslaby@suse.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/3] tty: Use RCU read lock to iterate tasks and threads in __do_SAK()
Date: Wed, 17 Jan 2018 18:39:55 +0100 [thread overview]
Message-ID: <20180117173955.GB7964@redhat.com> (raw)
In-Reply-To: <87lggwh1ef.fsf@xmission.com>
On 01/17, Eric W. Biederman wrote:
>
> __do_SAK() needs to be 100% accurate.
But it can't. A process/thread can open tty right after the check.
> I do not see the rcu_read_lock
> guaranteeing that new processes created while the process list is being
> iterated that happen to have a reference to the tty will be seen.
We can't miss the new child if its parent has this tty opened at fork() time,
__do_SAK() sends SIGKILL and ->siglock serializes __do_SAK() with copy_process()
which checks signal_pending() under the same ->siglock. So either fork() should
fail or for_each_process() should see the new child.
Right?
Otherwise we do not care. The child can open tty later but this doesn't differ
from the "race" above.
Oleg.
next prev parent reply other threads:[~2018-01-17 17:39 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-17 12:39 [PATCH v2 0/3] tty: Make __do_SAK() less greedy in regard to tasklist_lock Kirill Tkhai
2018-01-17 12:39 ` [PATCH v2 1/3] Revert "do_SAK: Don't recursively take the tasklist_lock" Kirill Tkhai
2018-01-17 17:18 ` Eric W. Biederman
2018-01-17 17:34 ` Oleg Nesterov
2018-01-17 17:49 ` Eric W. Biederman
2018-01-17 18:04 ` Oleg Nesterov
2018-01-17 18:37 ` Eric W. Biederman
2018-01-17 20:43 ` Oleg Nesterov
2018-01-18 10:07 ` Kirill Tkhai
2018-01-18 9:59 ` Kirill Tkhai
2018-01-17 12:39 ` [PATCH v2 2/3] tty: Avoid threads files iterations in __do_SAK() Kirill Tkhai
2018-01-17 12:39 ` [PATCH v2 3/3] tty: Use RCU read lock to iterate tasks and threads " Kirill Tkhai
2018-01-17 16:54 ` Eric W. Biederman
2018-01-17 17:39 ` Oleg Nesterov [this message]
2018-01-18 10:11 ` Kirill Tkhai
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