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Date:   Mon, 7 Jun 2021 17:54:33 -0500
From:   Segher Boessenkool <segher@kernel.crashing.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Alexander Monakov <amonakov@ispras.ru>,
        Jakub Jelinek <jakub@redhat.com>,
        Alan Stern <stern@rowland.harvard.edu>,
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Subject: Re: [RFC] LKMM: Add volatile_if()
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On Mon, Jun 07, 2021 at 01:31:24PM -0700, Linus Torvalds wrote:
> > Is it useful in general for the kernel to have separate "read" and
> > "write" clobbers in asm expressions?  And for other applications?
> 
> See above. It's actually not all that uncommon that you have a "this
> doesn't modify memory, but you can't move writes around it". It's
> usually very much about cache handling or memory ordering operations,
> and that bit test example was probably a bad example exactly because
> it made it look like it's about some controlled range.
> 
> The "write memory barroer" is likely the best and simplest example,
> but it's in not the only one.

Thanks for the examples!  I opened <https://gcc.gnu.org/PR100953> so
that we can easily track it.


Segher