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Date: Thu, 6 Jun 2019 10:11:41 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>,
Will Deacon <will.deacon@....com>,
Thomas Gleixner <tglx@...utronix.de>,
Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
the arch/x86 maintainers <x86@...nel.org>,
Davidlohr Bueso <dave@...olabs.net>,
Tim Chen <tim.c.chen@...ux.intel.com>,
huang ying <huang.ying.caritas@...il.com>, dvyukov@...gle.com,
glider@...gle.com, aryabinin@...tuozzo.com
Subject: Re: [PATCH v8 15/19] locking/rwsem: Adaptive disabling of reader
optimistic spinning
On Thu, Jun 06, 2019 at 10:03:15AM +0200, Peter Zijlstra wrote:
> On Wed, Jun 05, 2019 at 01:52:15PM -0700, Linus Torvalds wrote:
> > On Wed, Jun 5, 2019 at 1:19 PM Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > Urgh, that's another things that's been on the TODO list for a long long
> > > time, write code to verify the alignment of allocations :/ I'm
> > > suspecting quite a lot of that goes wrong all over the place.
> >
> > On x86, we only guarantee 8-byte alignment from things like kmalloc(), iirc.
>
> Oh sure, and I'm not proposing to change that. I was more thinking of
> having a GCC plugin that verifies, for every ptr assignment:
>
> ptr = foo;
To better qualify: 'for every ptr assignment that includes a type cast',
and since allocators return 'void *' and (typically/eventually) assign
to a typed pointer, that would be the place to check.
This avoids having to instrument every single pointer assignment.
> that the actual alignment maches:
>
> assert(!(uintptr_t)ptr % __alignof(*ptr));
>
> That would catch bugs like:
>
> struct bar {
> int ponies;
> int peaches __smp_cacheline_aligned;
> };
>
> struct bar *barp = kmalloc(sizeof(barp, GFP_KERNEL);
>
> Blatantly violating alignment can't be right; either the alignment
> constraints put on the data structures are not important and they should
> be fixed, or we should respect them and fix the allocation, either way,
> we should not silently violate things like we do today.
>
>
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