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Message-ID: <4f6e9e8bf60f05872afaed4a1d8e516331e95ea7.camel@synopsys.com>
Date: Mon, 9 Jul 2018 14:53:36 +0000
From: Alexey Brodkin <Alexey.Brodkin@...opsys.com>
To: "peterz@...radead.org" <peterz@...radead.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"linux-snps-arc@...ts.infradead.org"
<linux-snps-arc@...ts.infradead.org>,
"stable@...r.kernel.org" <stable@...r.kernel.org>,
"will.deacon@....com" <will.deacon@....com>,
"greg@...ah.com" <greg@...ah.com>,
"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
"David.Laight@...LAB.COM" <David.Laight@...LAB.COM>,
Vineet Gupta <Vineet.Gupta1@...opsys.com>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
"geert@...ux-m68k.org" <geert@...ux-m68k.org>
Subject: Re: [PATCH v3] devres: Explicitly align datai[] to 64-bit
Hi Peter,
On Mon, 2018-07-09 at 16:49 +0200, Peter Zijlstra wrote:
> On Mon, Jul 09, 2018 at 02:33:26PM +0000, Alexey Brodkin wrote:
> > > In fact, since alloc_dr() uses kmalloc() to allocate the entire thing,
> > > it is impossible to guarantee a larger alignment than kmalloc does.
> >
> > Well but 4-bytes [which is critical for atomic64_t] should be much less
> > than a sane cache line length so above should work.
>
> AFAICT ARCH_KMALLOC_MINALIGN ends up being 4 on x86_32 (it doesn't
> define ARCH_DMA_MINALIGN and doesn't seem to otherwise override the
> thing).
>
> So unconditionally setting the alignment of devres::data to 8 seems
> broken.
Well but then what other options do we have to fix a problem with
misaligned access to atomic64_t in drm_gpu_scheduler?
-Alexey
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