From: pwaechtler@mac•com (Peter Waechtler)
To: linux-arm-kernel@lists•infradead.org
Subject: ARM11MPcore: tlb_ops_need_broadcast causes deadlock
Date: Sun, 25 Mar 2012 22:22:49 +0200 [thread overview]
Message-ID: <4F6F7E99.1020500@mac.com> (raw)
In-Reply-To: <20120325191556.GA3147@n2100.arm.linux.org.uk>
On 25.03.2012 21:15, Russell King - ARM Linux wrote:
> On Sun, Mar 25, 2012 at 08:22:05PM +0200, Peter Waechtler wrote:
>> On 25.03.2012 15:09, Russell King - ARM Linux wrote:
>>> On Sun, Mar 25, 2012 at 12:08:47PM +0000, Peter Waechtler wrote:
>>>> But Will, is that tlb_flush necessary at all? The ARM has only 3 permission
>>>> bits in the page table (APX and AP0 and AP1). The young/accessed bit is done
>>>> via software.
>>> Yes it most definitely is, because setting a page to be young means we
>>> must receive a subsequent fault to make it 'old' again. This means we
>>> must set the page to be inaccessible to get that fault, and flush the
>>> TLBs across all CPUs so that any CPU accessing that page receives a
>>> fault.
>> Ok I see, it's also not the "right or perfect" fix.
> It's not a fix or anything, it's required behaviour - otherwise we could
> end up throwing out pages from the system which are actually 'hot' because
> they've stayed in the TLB and we haven't received a fault to make them
> young again.
I'm arguing solely on kswapd making a young page old. So it can't be a
hot page.
But yes in theory it's possible that it just become hot on another cpu...
And again I don't understand the abort handler: why do we get a page
fault on
a young page then? grrh
> Moreover, what about the case where we actually remove the page?
I don't claim that this is the only way to deadlock - but this is the
case we encounter.
> Aren't we also holding the pte lock there? So I don't think there's an
> obvious solution to your deadlock.
>
> I think the real question is - in your example - why are you touching
> a userspace page with IRQs off _and_ expecting the fault to be fixed up?
> You never really explained what CPU B was doing.
It was running some user space program. It was not in the kernel.
I will post the jtag probe screenshots tomorrow.
Peter
next prev parent reply other threads:[~2012-03-25 20:22 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-22 12:24 ARM11MPcore: tlb_ops_need_broadcast causes deadlock EXTERNAL Waechtler Peter (Fa. TCP, CM-AI/PJ-CF31)
2012-03-23 17:30 ` Will Deacon
2012-03-25 12:08 ` Peter Waechtler
2012-03-25 13:09 ` Russell King - ARM Linux
2012-03-25 18:22 ` Peter Waechtler
2012-03-25 19:15 ` Russell King - ARM Linux
2012-03-25 20:22 ` Peter Waechtler [this message]
2012-03-25 21:55 ` Russell King - ARM Linux
2012-03-26 15:20 ` Will Deacon
[not found] ` <274124B9C6907D4B8CE985903EAA19E91B2D5798D9@SI-MBX06.de.bosch.com>
2012-03-27 13:32 ` Will Deacon
2012-03-27 17:41 ` George G. Davis
2012-03-28 8:56 ` Will Deacon
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