linux-kernel - Re: [PATCH v4] mm: per-thread vma caching

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Date:	Thu, 13 Mar 2014 21:43:08 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	Davidlohr Bueso <davidlohr@...com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Michel Lespinasse <walken@...gle.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>,
	linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] mm: per-thread vma caching

On Fri, 14 Mar 2014 11:05:51 +0800 Li Zefan <lizefan@...wei.com> wrote:

> Hi Davidlohr,
> 
> On 2014/3/4 11:26, Linus Torvalds wrote:
> > On Mon, Mar 3, 2014 at 7:13 PM, Davidlohr Bueso <davidlohr@...com> wrote:
> >>
> >> Yes, I shortly realized that was silly... but I can say for sure it can
> >> happen and a quick qemu run confirms it. So I see your point as to
> >> asking why we need it, so now I'm looking for an explanation in the
> >> code.
> > 
> > We definitely *do* have users.
> > 
> > One example would be ptrace -> access_process_vm -> __access_remote_vm
> > -> get_user_pages() -> find_extend_vma() -> find_vma_prev -> find_vma.
> > 
> 
> I raw this oops on 3.14.0-rc5-next-20140307, which is possible caused by
> your patch? Don't know how it was triggered.
> 
> ...
>
> [ 6072.027007]  [<ffffffff811a4f62>] get_user_pages+0x52/0x60
> [ 6072.027015]  [<ffffffff811a5088>] __access_remote_vm+0x118/0x1f0
> [ 6072.027023]  [<ffffffff811a51bb>] access_process_vm+0x5b/0x80
> [ 6072.027033]  [<ffffffff812675a7>] proc_pid_cmdline+0x77/0x120
> [ 6072.027041]  [<ffffffff81267da2>] proc_info_read+0xa2/0xe0
> [ 6072.027050]  [<ffffffff811f439d>] vfs_read+0xad/0x1a0
> [ 6072.027057]  [<ffffffff811f45b5>] SyS_read+0x65/0xb0
> [ 6072.027066]  [<ffffffff8159ba12>] system_call_fastpath+0x16/0x1b
> [ 6072.027072] Code: f4 4c 89 f7 89 45 a4 e8 36 0e eb ff 48 3d 00 f0 ff ff 48 89 c3 0f 86 d7 00 00 00 4c 89 e0
>  49 8b 56 40 48 c1 e8 27 25 ff 01 00 00 <48> 8b 0c c2 48 85 c9 75 3e 41 83 e5 08 74 1b 49 8b 87 90 00 00
> [ 6072.027134] RIP  [<ffffffff811a0189>] follow_page_mask+0x69/0x620
> [ 6072.027142]  RSP <ffff880618855c18>
> [ 6072.027146] CR2: 00000000000007f8

Yep.  Please grab whichever of

mm-per-thread-vma-caching-fix-3.patch
mm-per-thread-vma-caching-fix-4.patch
mm-per-thread-vma-caching-fix-5.patch
mm-per-thread-vma-caching-fix-6-checkpatch-fixes.patch
mm-per-thread-vma-caching-fix-6-fix.patch

which you don't have from http://ozlabs.org/~akpm/mmots/broken-out/
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