From: "Michael S. Tsirkin" <mst@redhat.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: linux-arch@vger.kernel.org, heiko.carstens@de.ibm.com,
linux-kernel@vger.kernel.org,
David Hildenbrand <dahi@linux.vnet.ibm.com>,
paulus@samba.org, schwidefsky@de.ibm.com,
akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org,
mingo@kernel.org
Subject: Re: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic
Date: Wed, 26 Nov 2014 19:21:39 +0200 [thread overview]
Message-ID: <20141126172139.GA11746@redhat.com> (raw)
In-Reply-To: <20141126170447.GC11202@redhat.com>
On Wed, Nov 26, 2014 at 07:04:47PM +0200, Michael S. Tsirkin wrote:
> On Wed, Nov 26, 2014 at 05:51:08PM +0100, Christian Borntraeger wrote:
> > > But this one was > giving users in field false positives.
> >
> > So lets try to fix those, ok? If we cant, then tough luck.
>
> Sure.
> I think the simplest way might be to make spinlock disable
> premption when CONFIG_DEBUG_ATOMIC_SLEEP is enabled.
Specifically maybe DEBUG_ATOMIC_SLEEP should select PREEMPT_COUNT?
> As a result, userspace access will fail and caller will
> get a nice error.
>
>
>
> > But coming up with wrong statements is not helpful.
>
> True. Sorry that I did that.
>
> > >
> > > The point is that *_user is safe with preempt off.
> > > It returns an error gracefully.
> > > It does not sleep.
> > > It does not trigger the scheduler in that context.
> >
> > There are special cases where your statement is true. But its not in general.
> > copy_to_user might fault and that fault might sleep and reschedule.
>
> Yes. But not if called inatomic.
>
>
>
> > For example handle_mm_fault might go down to pud_alloc, pmd_alloc etc and all these functions could do an GFP_KERNEL allocation. Which might sleep. Which will schedule.
> >
> >
> > >
> > >
> > > David's patch makes it say it does, so it's wrong.
> > >
> > >
> > >
>
> Absolutely.
> I think you can already debug your case easily, by enabling CONFIG_PREEMPT.
> This seems counter-intuitive, and distro debug kernels don't seem to do this.
>
> --
> MST
next prev parent reply other threads:[~2014-11-26 17:22 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-25 11:43 [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic David Hildenbrand
2014-11-25 11:43 ` [RFC 1/2] powerpc/fsl-pci: atomic get_user when pagefault_disabled David Hildenbrand
2015-01-30 5:15 ` [RFC,1/2] " Scott Wood
2015-01-30 7:58 ` David Hildenbrand
2014-11-25 11:43 ` [RFC 2/2] mm, sched: trigger might_sleep() in might_fault() when atomic David Hildenbrand
2014-11-26 7:02 ` [RFC 0/2] Reenable might_sleep() checks for " Michael S. Tsirkin
2014-11-26 10:05 ` David Hildenbrand
2014-11-26 15:17 ` Michael S. Tsirkin
2014-11-26 15:23 ` Michael S. Tsirkin
2014-11-26 15:32 ` David Hildenbrand
2014-11-26 15:47 ` Michael S. Tsirkin
2014-11-26 16:02 ` David Hildenbrand
2014-11-26 16:19 ` Michael S. Tsirkin
2014-11-26 16:30 ` Christian Borntraeger
2014-11-26 16:50 ` Michael S. Tsirkin
2014-11-26 16:07 ` Christian Borntraeger
2014-11-26 16:32 ` Michael S. Tsirkin
2014-11-26 16:51 ` Christian Borntraeger
2014-11-26 17:04 ` Michael S. Tsirkin
2014-11-26 17:21 ` Michael S. Tsirkin [this message]
2014-11-27 7:09 ` Heiko Carstens
2014-11-27 7:40 ` Michael S. Tsirkin
2014-11-27 8:03 ` David Hildenbrand
2014-11-27 12:04 ` Heiko Carstens
2014-11-27 12:08 ` David Hildenbrand
2014-11-27 15:07 ` Thomas Gleixner
2014-11-27 15:19 ` David Hildenbrand
2014-11-27 15:37 ` David Laight
2014-11-27 15:45 ` David Hildenbrand
2014-11-27 16:27 ` David Laight
2014-11-27 16:49 ` David Hildenbrand
2014-11-27 21:52 ` Thomas Gleixner
2014-11-28 7:34 ` David Hildenbrand
2014-11-26 15:30 ` Christian Borntraeger
2014-11-26 15:37 ` Michael S. Tsirkin
2014-11-26 16:02 ` Christian Borntraeger
2014-11-26 15:22 ` Michael S. Tsirkin
2014-11-27 17:10 ` [PATCH RFC " David Hildenbrand
2014-11-27 17:10 ` [PATCH RFC 1/2] preempt: track pagefault_disable() calls in the preempt counter David Hildenbrand
2014-11-27 17:10 ` [PATCH RFC 2/2] mm, sched: trigger might_sleep() in might_fault() when pagefaults are disabled David Hildenbrand
2014-11-27 17:24 ` Michael S. Tsirkin
2014-11-27 17:32 ` Michael S. Tsirkin
2014-11-27 18:08 ` David Hildenbrand
2014-11-27 18:27 ` Michael S. Tsirkin
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