linux-kernel - Re: [PATCH 2/2] coredump: exit_mm: clear ->mm first, then play with ->core

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Date:	Sun, 20 Jul 2008 17:08:42 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] coredump: exit_mm: clear ->mm first, then play with ->core_state

> Yes, oom_kill.c in turn need fixes but still this is not nice, and I
> personally hate this coredump code in the middle of exit_mm().

I agree.  I think what we should work towards is having the coredump
synchronization take place earlier (the tracehook_report_exit point should
be fine, i.e. before PF_EXITING).  Then have the dumping and the waiting
for it be killable.  I don't think we can get there in only one or two
steps, though.

[The rest if quite off-topic, please do it separately.]

> btw, arch/sparc64/kernel/ptrace.c has a lot of
> 
> 	if (target == current)
> 		copy_xxx_user();
> 	else
> 		access_process_vm();
> 
> perhaps it make sense to make a helper. 

Dave actually has get_from_target and set_to_target helpers for that.
The places they aren't used, I assume are either just older code not
yet streamlined, or places where the separate get/put_user calls perform
especially better than copy_xxx_user (you'd have to ask Dave).  If multiple
arch ports find such helpers useful, they could move into common code later.

> Just curious (I don't know what regset is), is it possible that ->get()
> is called when target->mm == NULL?

It should not happen.  It's only kosher to use user_regset calls on a task
in a known state (like ptrace stop, or current), and never on kernel threads.

Thanks,
Roland
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