Re: [Xen-devel] [PATCH] KVM, XEN: Fix potential race in pvclock code

[Julian Stecklina <jsteckli@xxxxxxxxxxxxxxxxxxxx>]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 01/28/2014 04:16 PM, Konrad Rzeszutek Wilk wrote:
>> At least 4.8 and probably older compilers compile this as
>> intended. The point is that the standard does not guarantee the
>> indented behavior, i.e. the code is wrong.
> 
> Perhaps I misunderstood Jan's response but it sounded to me like 
> that the compiler was not adhering to the standard?

Compilers are free to generate code that breaks the current clock code
while staying within the standards. If the compiler ignores the
standard, all bets are off anyway...

>> 
>> I can refer to this lwn article: 
>> https://lwn.net/Articles/508991/
>> 
>> The whole point of ACCESS_ONCE is to avoid time bombs like that.
>> There are lots of place where ACCESS_ONCE is used in the kernel:
>> 
>> http://lxr.free-electrons.com/ident?i=ACCESS_ONCE
>> 
>> See for example the check_zero function here: 
>> http://lxr.free-electrons.com/source/arch/x86/kernel/kvm.c#L559
>> 
> 
> In other words, you don't have a sample of 'bad' compiler code.

Nope.

Julian

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.22 (GNU/Linux)

iEUEARECAAYFAlLn1ZgACgkQ2EtjUdW3H9n/DgCSAmrVCyxrs42aFFB3Ug+aw4kN
7wCgmEO4CbOI3BkOXKSorY91td9u7H8=
=fgrl
-----END PGP SIGNATURE-----

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel