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Subject: Re: patch: do_wait: make PIDTYPE_PID case O(1) instead of O(n)
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Christian Brauner <christian@brauner.io>,
        linux-kernel@vger.kernel.org
References: <b8591e67-1248-6c29-847e-d97e04b58210@torproject.org>
 <20210309085641.GB25222@redhat.com>
From:   Jim Newsome <jnewsome@torproject.org>
Organization: The Tor Project
Message-ID: <383ff3ab-ef13-1c6e-7794-ecfffc6044d4@torproject.org>
Date:   Tue, 9 Mar 2021 10:18:18 -0600
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Thanks for the quick review!

On 3/9/21 02:56, Oleg Nesterov wrote:
> I'd suggest to put this PIDTYPE_PID code into the new function.

Done

> No, you don't need rcu lock, tasklist_lock is sufficient

Done

> This is wrong, you forgot to drop tasklist_lock.

Done

>> +		real_parent = !target->real_parent ? target->parent :
>> +						     target->real_parent;
> 
> Hmm, I don't understand the line above... perhaps it connects to the
> question below.

I'd mistakenly thought `real_parent` was NULL if the target wasn't being
traced (or was being traced by the real parent). It looks like indeed
this should always be set, though.

> Afaics, parent/real_parent can't be NULL if pid_task() succeeds.

Done

> Please redo and send V2 ;)

Sent with subject "[PATCH v2] do_wait: make PIDTYPE_PID case O(1)
instead of O(n)"