Re: ARC stable backport request
On Mon, Aug 15, 2016 at 06:42:45AM +, Alexey Brodkin wrote: > Hi Greg, > > On Sun, 2016-08-14 at 17:39 +0200, Greg KH wrote: > > On Wed, May 25, 2016 at 05:13:31PM +0530, Vineet Gupta wrote: > > > > > > Hi, > > > > > > Can we please backport a6416f57ce57fb390b "ARC: use ASL assembler > > > mnemonic". > > > Newer binutils don't like ASL instruction and fail to build kernels prior > > > to v4.4 > > > which added this fix. > > > > Fails to apply to 3.14-stable :( > > Looks like it's there already. Isn't it? > http://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/arch/arc?h=linux-3.14.y&id=8ba2f5328c2c9859bb > bf412e5804974483d66e9d Doh! Sorry for the noise, my fault... greg k-h ___ linux-snps-arc mailing list linux-snps-arc@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-snps-arc
Re: [RESEND PATCH v2] devres: Really align data field to unsigned long long
On Mon, Jul 09, 2018 at 06:46:50AM +, Alexey Brodkin wrote:
> Hi Greg,
>
> On Mon, 2018-07-09 at 07:48 +0200, Greg KH wrote:
> > On Mon, Jul 09, 2018 at 07:44:44AM +0300, Alexey Brodkin wrote:
> > > Depending on ABI "long long" type of a particular 32-bit CPU
> > > might be aligned by either word (32-bits) or double word (64-bits).
> > > Make sure "data" is really 64-bit aligned for any 32-bit CPU.
> > >
> > > At least for 32-bit ARC cores ABI requires "long long" types
> > > to be aligned by normal 32-bit word. This makes "data" field aligned to
> > > 12 bytes. Which is still OK as long as we use 32-bit data only.
> > >
> > > But once we want to use native atomic64_t type (i.e. when we use special
> > > instructions LLOCKD/SCONDD for accessing 64-bit data) we easily hit
> > > misaligned access exception.
> >
> > So is this something you hit today? If not, why is this needed for
> > stable kernels?
>
> Indeed we hit that problem recently when Etnaviv driver was switched to
> DRM GPU scheduler, see
> commit e93b6deeb45a ("drm/etnaviv: hook up DRM GPU scheduler").
> The most important part of DRM GPU scheduler is "job_id_count" member of
> "drm_gpu_scheduler" structure of type "atomic64_t". This structure is put
> in a buffer allocated by devm_kzalloc() and if "job_id_count" is not 64-bit
> aligned atomic instruction fails with an exception.
>
> As for stable requirements - mentioned commit was a part of 4.17 kernel
> which broke GPU driver for one of our HSDK board so I guess back-porting
> to 4.17 is a no-brainer.
Ok, so 4.17 is as far back as you need? Please try to be specific when
asking for stable backports.
> > > That's because even on CPUs capable of non-aligned data access LL/SC
> > > instructions require strict alignment.
> >
> > Are you going to hit this code with all types of structures?
>
> If there're other cases which lead to 4-byte aligned "atomic64_t" variables
> there will be a problem as well but it's quite hard to predict those cases.
> That said if we manage to reproduce more similar issues there will be more
> patches with fixes :)
>
> > What happens when you do have an unaligned access?
>
> Atomic instructions are a bit special as compared to normal loads and stores.
> Even if normal loads and stores may deal with unaligned data atomic
> instructions
> still require data to be aligned because it's hard to manage atomic value that
> spans through multiple cache lines or even MMU pages. And hardware just
> raises an alignment fault exception.
>
> And that's not something special for ARC, I guess all CPUs are the same in
> that regard, see here's an extract from ARM(r) Architecture Reference
> Manual ARMv7-A and ARMv7-R edition: https://lkml.org/lkml/2017/12/5/440
> From "Table A3-1 Alignment requirements of load/store instructions"
> it's seen that LDREXD, STREXD instructions will cause alignment fault
> even if SCTLR.A=0 (strict alignment fault checking disabled) for non
> double-word-aligned data.
Thanks for the better explaination, that helps out a lot. Can you redo
the patch with all of that information so that others do not have the
same questions as I did?
thanks,
greg k-h
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Re: [RESEND PATCH v2] devres: Really align data field to unsigned long long
On Mon, Jul 09, 2018 at 07:17:11AM +, Alexey Brodkin wrote:
> Hi Greg,
>
> On Mon, 2018-07-09 at 09:06 +0200, g...@kroah.com wrote:
> > On Mon, Jul 09, 2018 at 06:46:50AM +, Alexey Brodkin wrote:
> > > Hi Greg,
> > >
> > > On Mon, 2018-07-09 at 07:48 +0200, Greg KH wrote:
> > > > On Mon, Jul 09, 2018 at 07:44:44AM +0300, Alexey Brodkin wrote:
> > > > > Depending on ABI "long long" type of a particular 32-bit CPU
> > > > > might be aligned by either word (32-bits) or double word (64-bits).
> > > > > Make sure "data" is really 64-bit aligned for any 32-bit CPU.
> > > > >
> > > > > At least for 32-bit ARC cores ABI requires "long long" types
> > > > > to be aligned by normal 32-bit word. This makes "data" field aligned
> > > > > to
> > > > > 12 bytes. Which is still OK as long as we use 32-bit data only.
> > > > >
> > > > > But once we want to use native atomic64_t type (i.e. when we use
> > > > > special
> > > > > instructions LLOCKD/SCONDD for accessing 64-bit data) we easily hit
> > > > > misaligned access exception.
> > > >
> > > > So is this something you hit today? If not, why is this needed for
> > > > stable kernels?
> > >
> > > Indeed we hit that problem recently when Etnaviv driver was switched to
> > > DRM GPU scheduler, see
> > > commit e93b6deeb45a ("drm/etnaviv: hook up DRM GPU scheduler").
> > > The most important part of DRM GPU scheduler is "job_id_count" member of
> > > "drm_gpu_scheduler" structure of type "atomic64_t". This structure is put
> > > in a buffer allocated by devm_kzalloc() and if "job_id_count" is not
> > > 64-bit
> > > aligned atomic instruction fails with an exception.
> > >
> > > As for stable requirements - mentioned commit was a part of 4.17 kernel
> > > which broke GPU driver for one of our HSDK board so I guess back-porting
> > > to 4.17 is a no-brainer.
> >
> > Ok, so 4.17 is as far back as you need? Please try to be specific when
> > asking for stable backports.
>
> Well in that particular case I really wanted to get this fix back-ported
> starting from v4.8 so I guess that's what I need to add in Cc tag, right?
> ->8-
> Cc: # 4.8+
> ->8-
Yes.
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