linux-kernel - Re: [PATCH][V3]Make get_user

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Message-ID: <84144f020811241313o7401e3c2gd360c4226f33b28f@mail.gmail.com>
Date:	Mon, 24 Nov 2008 23:13:10 +0200
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Ying Han" <yinghan@...gle.com>
Cc:	"Paul Menage" <menage@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, akpm <akpm@...ux-foundation.org>,
	"David Rientjes" <rientjes@...gle.com>,
	"Rohit Seth" <rohitseth@...gle.com>
Subject: Re: [PATCH][V3]Make get_user_pages interruptible

On Fri, Nov 21, 2008 at 5:31 PM, Ying Han <yinghan@...gle.com> wrote:
>>>                         */
>>> -                       if (unlikely(test_tsk_thread_flag(tsk, TIF_MEMDIE)))
>>> -                               return i ? i : -ENOMEM;
>>> +                       if (unlikely(sigkill_pending(tsk)))
>>> +                               return i ? i : -ERESTARTSYS;

On Mon, Nov 24, 2008 at 12:02 PM, Paul Menage <menage@...gle.com> wrote:
>> You've changed the check from sigkill_pending(current) to sigkill_pending(tsk).
>>
>> I originally made that sigkill_pending(current) since we want to avoid
>> tasks entering an unkillable state just because they're doing
>> get_user_pages() on a system that's short of memory. Admittedly for
>> the main case that we care about, mlock() (or an mmap() with
>> MCL_FUTURE set) then tsk==current, but philosophically it seems to me
>> to be more correct to do the check against current than tsk, since
>> current is the thing that's actually allocating the memory. But maybe
>> it would be better to check both?

On Mon, Nov 24, 2008 at 11:02 PM, Ying Han <yinghan@...gle.com> wrote:
> In most of cases, tsk==current in get_user_pages(), that is why i
> change current to tsk since
> tsk is a superset of current, no? If that is right, why we need to check both?

I'm not sure if it's strictly necessary but as I pointed out in the
other mail, there can be callers that are doing get_user_pages() on
behalf of other tasks and you probably want to be able to kill the
task that's actually _calling_ get_user_pages() as well.

                        Pekka
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