linux-kernel - Re: [PATCH] sched, arm64: Fix the fallout of increasing the offset of 'thread_struct' within 'task

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Message-ID: <20150720140355.GM20385@e104818-lin.cambridge.arm.com>
Date:	Mon, 20 Jul 2015 15:03:55 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-s390@...r.kernel.org,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Olof Johansson <olof@...om.net>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux390@...ibm.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] sched, arm64: Fix the fallout of increasing the offset
 of 'thread_struct' within 'task_struct'

On Mon, Jul 20, 2015 at 06:52:28AM -0700, Guenter Roeck wrote:
> On 07/20/2015 12:20 AM, Ingo Molnar wrote:
> >* Guenter <linux@...ck-us.net> wrote:
> >>On Sat, Jul 18, 2015 at 04:27:17PM -0700, Guenter wrote:
> >>>Commit 0c8c0f03e3a2 ("x86/fpu, sched: Dynamically allocate 'struct fpu'")
> >>>causes s390 builds in mainline to fail as follows.
> >>>
> >>>arch/s390/kernel/traps.c: Assembler messages:
> >>>arch/s390/kernel/traps.c:262: Error: operand out of range
> >>>	(0x00000000000023e8 is not between 0x0000000000000000 and 0x0000000000000fff)
> >>>arch/s390/kernel/traps.c:300: Error: operand out of range
> >>>	(0x00000000000023e8 is not between 0x0000000000000000 and 0x0000000000000fff)
> >>>
> >>
> >>Also:
> >>
> >>arm64:allmodconfig:
> >>
> >>arch/arm64/kernel/entry.S: Assembler messages:
> >>arch/arm64/kernel/entry.S:588: Error: immediate out of range
> >>arch/arm64/kernel/entry.S:597: Error: immediate out of range
> >>make[1]: *** [arch/arm64/kernel/entry.o] Error 1
> >>
> >>I didn't bisect that one, but it looks like the cause is the same.
> >
> >Hm, it looks like the new, increased offset of 'thread_struct' within
> >'task_struct' goes over a limit that these instructions are able to support on
> >arm64:
> >
> >  arch/arm64/kernel/asm-offsets.c:  DEFINE(THREAD_CPU_CONTEXT,    offsetof(struct task_struct, thread.cpu_context));
> >  arch/arm64/kernel/entry.S:      add     x8, x0, #THREAD_CPU_CONTEXT
> >  arch/arm64/kernel/entry.S:      add     x8, x1, #THREAD_CPU_CONTEXT
> >
> >If there's no instruction that can support such offset sizes then I suspect the
> >straightforward fix would be to pass in thread_struct instead - like the patch
> >below. That's a tiny bit cleaner for type encapsulation anyway.
> 
> Olof submitted a different patch to solve the problem:
> 	http://www.spinics.net/lists/kernel/msg2036825.html
> 
> His patch is passing cpu_context instead of thread_context.

It's likely that we'll use this patch instead:

http://lkml.kernel.org/g/20150720105345.GC9908@arm.com

-- 
Catalin
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