linux-kernel - Re: A bug about system call on ARM

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Date:	Thu, 30 May 2013 10:09:49 +0100
From:	Will Deacon <will.deacon@....com>
To:	"Wang, Yalin" <Yalin.Wang@...ymobile.com>
Cc:	"'richard -rw- weinberger'" <richard.weinberger@...il.com>,
	"'linux-arch@...r.kernel.org'" <linux-arch@...r.kernel.org>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'linux-arm-kernel@...ts.infradead.org'" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: A bug about system call on ARM

On Thu, May 30, 2013 at 02:41:42AM +0100, Wang, Yalin wrote:
> Hi  Will,

Hello,

> Have you received the log files?

Yep, and you seem to be completely correct: CPU0 ages the page from which
CPU1 just executed a system call, so we explode trying to load the swi
instruction in order to retrieve the immediate.

> And is there someone looking at this issue now ?

It's on my list, but I'm pretty busy right now and OABI-compat isn't high
priority. Are you actually running OABI binaries? If not, you can simply
turn that option off (in fact, a quick fix to this issue is to make that
depend on !SMP).

> This issue happened on Qcom Scorpoin CPUs,
> And  it just happened in our stability test occasionally .
> 
> If you have some patch for this issue,
> I can do the test for it .

I'll have a look at cooking something which uses an exception table entry
to rewind the PC and retry the system call. That's simpler than directly
injecting a user page fault from the system call path.

Will
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