From: David Hildenbrand <dahi@linux.vnet.ibm.com>
To: David Laight <David.Laight@ACULAB.COM>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"Michael S. Tsirkin" <mst@redhat.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"mingo@kernel.org" <mingo@kernel.org>,
Christian Borntraeger <borntraeger@de.ibm.com>,
"paulus@samba.org" <paulus@samba.org>,
"schwidefsky@de.ibm.com" <schwidefsky@de.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic
Date: Thu, 27 Nov 2014 17:49:25 +0100 [thread overview]
Message-ID: <20141127174925.53e9d7a6@thinkpad-w530> (raw)
In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D1C9FDDD6@AcuExch.aculab.com>
> From: David Hildenbrand [mailto:dahi@linux.vnet.ibm.com]
> > > From: David Hildenbrand
> > > ...
> > > > Although it might not be optimal, but keeping a separate counter for
> > > > pagefault_disable() as part of the preemption counter seems to be the only
> > > > doable thing right now. I am not sure if a completely separated counter is even
> > > > possible, increasing the size of thread_info.
> > >
> > > What about adding (say) 0x10000 for the more restrictive test?
> > >
> > > David
> > >
> >
> > You mean as part of the preempt counter?
> >
> > The current layout (on my branch) is
> >
> > * PREEMPT_MASK: 0x000000ff
> > * SOFTIRQ_MASK: 0x0000ff00
> > * HARDIRQ_MASK: 0x000f0000
> > * NMI_MASK: 0x00100000
> > * PREEMPT_ACTIVE: 0x00200000
> >
> > I would have added
> > * PAGEFAULT_MASK: 0x03C00000
>
> I'm not sure where you'd need to add the bits.
>
> I think the above works because disabling 'HARDIRQ' implicitly
> disables 'SOFTIRQ' and 'PREEMPT' (etc), so if 256+ threads
> disable PREEMPT everything still works.
AFAIK 256+ levels of preempt will break the system :)
Therefore with CONFIG_DEBUG_PREEMPT we verify that we don't have any
over/underflows.
But such bugs can only be found with CONFIG_DEBUG_PREEMPT enabled.
>
> So if disabling pagefaults implies that pre-emption is disabled
> (but SOFTIRQ is still allowed) then you need to insert your bit(s)
> between 0xff00 and 0x00ff.
> OTOH if disabling pre-emption implies that pagefaults are disabled
> then you'd need to use the lsb and change all the above values.
>
> Which makes me think that 'PREEMPT_ACTIVE' isn't right at all.
> Two threads disabling NMIs (or 32 disabling HARDIRQ) won't DTRT.
With threads you mean levels? This is a per thread information.
>
> OTOH I'm only guessing at how this is used.
>
> David
>
>
>
next prev parent reply other threads:[~2014-11-27 16:49 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
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 [this message]
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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