linux-kernel - Re: [PATCH 3.18 04/57] vm: add VM_FAULT

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Message-ID: <CALYGNiN6isfggY-kjWAgP1UtGyvKYN+BhWyuk9x6CF3wDe97HA@mail.gmail.com>
Date:	Wed, 11 Feb 2015 09:34:44 +0400
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Stable <stable@...r.kernel.org>,
	Jan Engelhardt <jengelh@...i.de>, linux-arch@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 3.18 04/57] vm: add VM_FAULT_SIGSEGV handling support

On Wed, Feb 11, 2015 at 6:43 AM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Tue, Feb 10, 2015 at 12:22:41PM +0400, Konstantin Khlebnikov wrote:
>> I've found regression:
>>
>> [  257.139907] ================================================
>> [  257.139909] [ BUG: lock held when returning to user space! ]
>> [  257.139912] 3.18.6-debug+ #161 Tainted: G     U
>> [  257.139914] ------------------------------------------------
>> [  257.139916] python/22843 is leaving the kernel with locks still held!
>> [  257.139918] 1 lock held by python/22843:
>> [  257.139920]  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff8104e4c2>]
>> __do_page_fault+0x162/0x570
>>
>> upstream commit 7fb08eca45270d0ae86e1ad9d39c40b7a55d0190 must be backported too.
>
> Ah, nice, I missed that one.  How did you test this?

I've catched hang on mmap_sem in some python self-test inside exherbo chroot.
With that patch test has finished successfully.

It seems the only way to tigger this is stack-overflow: for now VM_FAULT_SIGSEGV
is returned only if kernel cannot add guard page when stack expands.

>
> thanks,
>
> greg k-h
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