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

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Date:   Thu, 5 Mar 2020 16:48:12 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     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 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

> [1] http://lore.kernel.org/r/CAG48ez27=pwm5m_N_988xT1huO7g7h6arTQL44zev6TD-h-7Tg@mail.gmail.com
> 
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Jann Horn <jannh@...gle.com>
> Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
> Signed-off-by: Minchan Kim <minchan@...nel.org>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

Nit:

> @@ -676,7 +677,6 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
>  	if (nr_swap) {
>  		if (current->mm == mm)
>  			sync_mm_rss(mm);
> -
>  		add_mm_counter(mm, MM_SWAPENTS, nr_swap);
>  	}
>  	arch_leave_lazy_mmu_mode();

This looks stray and unrelated.