linux-kernel - Re: [PATCH 2/4] pid: Export find_task_by

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Message-ID: <87k1sdvczc.fsf@xmission.com>
Date:   Tue, 08 May 2018 20:23:19 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Kim Phillips <kim.phillips@....com>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Gargi Sharma <gs051095@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Rik van Riel <riel@...hat.com>,
        Robin Murphy <robin.murphy@....com>,
        Russell King <linux@...linux.org.uk>,
        Thierry Reding <treding@...dia.com>,
        Todd Kjos <tkjos@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] pid: Export find_task_by_vpid for use in external modules

Kim Phillips <kim.phillips@....com> writes:

> This patch is in the context of allowing the Coresight h/w
> trace driver suite to be loaded as modules.  Coresight uses
> find_task_by_vpid when running in direct capture mode (via sysfs)
> when getting/setting the context ID comparator to trigger on
> (/sys/bus/coresight/devices/<x>.etm/ctxid_pid).

Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

There is no way to implement a sysfs file that takes a pid correctly.
Don't do it.

Pids are tied to pid namespaces and sysfs deliberately does not do
anything remotely resembly a pid namespace.

Eric


> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Gargi Sharma <gs051095@...il.com>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Pavel Tatashin <pasha.tatashin@...cle.com>
> Cc: Kefeng Wang <wangkefeng.wang@...wei.com>
> Cc: Kirill Tkhai <ktkhai@...tuozzo.com>
> Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>
> Cc: David Howells <dhowells@...hat.com>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Signed-off-by: Kim Phillips <kim.phillips@....com>
> ---
> Current CoreSight callsite:
>
> https://lxr.missinglinkelectronics.com/linux/include/linux/coresight.h#L285
>
> A quick look didn't find anything, but if Coresight needs to do
> something differently, please comment.
>
>  kernel/pid.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 157fe4b19971..92b1b623f3e0 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -342,6 +342,7 @@ struct task_struct *find_task_by_vpid(pid_t vnr)
>  {
>  	return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
>  }
> +EXPORT_SYMBOL_GPL(find_task_by_vpid);
>  
>  struct task_struct *find_get_task_by_vpid(pid_t nr)
>  {