linux-kernel - Re: Hang on large copy_from_user with PREEMPT

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Date:	Tue, 7 Apr 2015 17:09:50 -0400
From:	Dave Jones <davej@...emonkey.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Borislav Petkov <bp@...en8.de>,
	Rusty Russell <rusty@...tcorp.com.au>,
	the arch/x86 maintainers <x86@...nel.org>,
	Michal Hocko <mhocko@...e.cz>, Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: Hang on large copy_from_user with PREEMPT_NONE

On Tue, Apr 07, 2015 at 11:12:31AM -0700, Linus Torvalds wrote:
 > On Apr 7, 2015 10:58 AM, "Dave Jones" <davej@...emonkey.org.uk> wrote:
 > >  >
 > >  > +#define COPY_CHUNK_SIZE (16*PAGE_SIZE)
 > >
 > > This needs to be bigger, just to accomodate things like xfs, which
 > > on my system is over 1mb.  I think some out-of-tree modules
 > > (not that I care deeply) are even bigger.
 > 
 > Umm. It will happily copy megabytes of data. Or gigabytes. It just doors it
 > in smaller chunks, and make sure to test the return value and possibly
 > reschedule in between.

brain no worky. You are of course, correct.

	Dave
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