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Date: Sat, 14 Apr 2012 05:39:53 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        David Howells <dhowells@redhat.com>,
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        Larry Woodman <lwoodman@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, Tejun Heo <tj@kernel.org>,
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Subject: Re: [PATCH v4 1/3] task_work_add: generic process-context callbacks
Message-ID: <20120414033953.GA29189@redhat.com>
References: <20120414021201.GA23385@redhat.com> <20120414021220.GA23393@redhat.com> <CA+55aFyxV8v2mOjb1Ly=1ttPyLvUt6RZO8wgjD_9owtO=VM0hw@mail.gmail.com>
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probably I should also comment this part...

On 04/13, Linus Torvalds wrote:
>
> Alternatively, you must make the rule be that the data can only be
> freed by the caller *if* it was returned from "task_work_cancel()".

Exactly.

Once the caller does task_work_add(twork), it no longer "owns" this
twork.

But, if task_work_cancel() succeeds - you own it again.

> But then you can't allocate it on the stack any more, and have to
> allocate it separately.

Yes, unless you do task_work_add/cancel(current).

Oleg.