linux-kernel - Re: [PATCH] drivers/usb: use READ_ONCE instead of deprecated ACCESS

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Message-ID: <20161120160940.GA31288@linux-80c1.suse>
Date:   Sun, 20 Nov 2016 08:09:40 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH] drivers/usb: use READ_ONCE instead of deprecated
 ACCESS_ONCE

Hi Greg!

On Sun, 20 Nov 2016, Greg KH wrote:

>On Sat, Nov 19, 2016 at 11:54:25AM -0800, Davidlohr Bueso wrote:
>> With the new standardized functions, we can replace all ACCESS_ONCE()
>> calls across relevant drivers/usb/.
>>
>> ACCESS_ONCE() does not work reliably on non-scalar types. For example
>> gcc 4.6 and 4.7 might remove the volatile tag for such accesses during
>> the SRA (scalar replacement of aggregates) step:
>>
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145
>>
>> Update the new calls regardless of if it is a scalar type, this is
>> cleaner than having three alternatives.
>>
>> Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
>
>Nit, this doesn't match your From: line :(

That's on purpose, and all my patches are the same.

>If this is the case, why not just replacing the define for ACCESS_ONCE()
>with READ_ONCE() and then go back and just do a search/replace for the
>whole kernel all at once?

So that we don't have three variants; the idea is to eventually
get rid of ACCESS_ONCE entirely.

>
>Or just send Linus a patch for this all at once after -rc1 is out?

No rush, whenever you see fit.

Thanks,
Davidlohr