linux-kernel - Re: [PATCH v7 3/7] mm: check fatal signal pending of target process

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Date:   Tue, 10 Mar 2020 15:24:08 -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
Subject: Re: [PATCH v7 3/7] mm: check fatal signal pending of target process

On Fri, Mar 06, 2020 at 11:22:07AM +0100, Vlastimil Babka wrote:
> On 3/2/20 8:36 PM, Minchan Kim wrote:
> > Bail out to prevent unnecessary CPU overhead if target process has
> > pending fatal signal during (MADV_COLD|MADV_PAGEOUT) operation.
> > 
> > Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
> > Signed-off-by: Minchan Kim <minchan@...nel.org>
> 
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> 
> Nit below:
> 
> > ---
> >  mm/madvise.c | 29 +++++++++++++++++++++--------
> >  1 file changed, 21 insertions(+), 8 deletions(-)
> > 
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index 349473fc6683..6543f2bfc3d8 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -36,6 +36,7 @@
> >  struct madvise_walk_private {
> >  	struct mmu_gather *tlb;
> >  	bool pageout;
> > +	struct task_struct *target_task;
> >  };
> >  
> >  /*
> > @@ -316,6 +317,10 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> >  	if (fatal_signal_pending(current))
> >  		return -EINTR;
> >  
> > +	if (private->target_task &&
> > +			fatal_signal_pending(private->target_task))
> > +		return -EINTR;
> 
> With madvise(2) private->target_task will be current, thus current will be
> tested twice. Not wrong, but maybe add a "private->target_task != current"
> condition?

It was in old series but removed because reviewer(IIRC, suren) wanted it.
I am not strong preference either way. Since you said it's nit and
considering other reviewer wanted to remove it, I will not change
further.

Thanks!