linux-kernel - Re: [PATCH v7 5/7] mm: support both pid and pidfd for process

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Message-ID: <14089609-5fb1-b082-716f-c2e129d27c48@suse.cz>
Date:   Fri, 6 Mar 2020 12:14:19 +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,
        Christian Brauner <christian@...uner.io>,
        Kirill Tkhai <ktkhai@...tuozzo.com>
Subject: Re: [PATCH v7 5/7] mm: support both pid and pidfd for process_madvise

On 3/2/20 8:36 PM, Minchan Kim wrote:
> There is a demand[1] to support pid as well pidfd for process_madvise
> to reduce unnecessary syscall to get pidfd if the user has control of
> the target process(ie, they could guarantee the process is not gone
> or pid is not reused).
> 
> This patch aims for supporting both options like waitid(2). So, the
> syscall is currently,
> 
> 	int process_madvise(int which, pid_t pid, void *addr,
> 		size_t length, int advise, unsigned long flag);

This is again halfway between kernel and userspace description, so if we stick
to userspace then it's:

 	int process_madvise(idtype_t idtype, id_t id, void *addr,
 		size_t length, int advice, unsigned long flags);


> @which is actually idtype_t for userspace libray and currently,
> it supports P_PID and P_PIDFD.
> 
> [1]  https://lore.kernel.org/linux-mm/9d849087-3359-c4ab-fbec-859e8186c509@virtuozzo.com/
> 
> Cc: Christian Brauner <christian@...uner.io>
> Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
> Suggested-by: Kirill Tkhai <ktkhai@...tuozzo.com>
> Signed-off-by: Minchan Kim <minchan@...nel.org>

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