linux-kernel - Re: [PATCH v7 1/7] mm: pass task and mm to do

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Message-ID: <20200508182143.GA101195@google.com>
Date:   Fri, 8 May 2020 11:21:43 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, linux-api@...r.kernel.org,
        oleksandr@...hat.com, Suren Baghdasaryan <surenb@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Dias <joaodias@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Jann Horn <jannh@...gle.com>,
        alexander.h.duyck@...ux.intel.com, sj38.park@...il.com,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v7 1/7] mm: pass task and mm to do_madvise

On Thu, Mar 05, 2020 at 04:48:12PM +0100, Vlastimil Babka wrote:
> On 3/2/20 8:36 PM, Minchan Kim wrote:
> > In upcoming patches, do_madvise will be called from external process
> > context so we shouldn't asssume "current" is always hinted process's
> > task_struct.
> 
> 
> > Furthermore, we couldn't access mm_struct via task->mm
> > once it's verified by access_mm which will be introduced in next
> > patch[1].
> 
> I would suggest to replace with:
> 
> Furthermore, we must not access mm_struct via task->mm, but obtain it via
> access_mm() once (in the following patch) and only use that pointer [1], so pass
> it to do_madvise() as well. Note the vma->vm_mm pointers are safe, so we can use
> them further down the call stack.
> 
> > And let's pass *current* and current->mm as arguments of
> > do_madvise so it shouldn't change existing behavior but prepare
> > next patch to make review easy.
> > 
> > Note: io_madvise pass NULL as target_task argument of do_madvise
> > because it couldn't know who is target.
> 
>              can't

Andrew already picked up your suggestion except "can't" part. I don't
think it's enough to resend fix it so I will leave it as-is.