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

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Date:   Fri, 6 Mar 2020 11:22:07 +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
Subject: Re: [PATCH v7 3/7] mm: check fatal signal pending of target process

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?