On Fri, Nov 02, 2018 at 07:19:15PM +0300, Andrey Ryabinin wrote:
> UBSAN warns about signed overflows despite -fno-strict-overflow if gcc
> version is < 8.
> I have learned recently that UBSAN in GCC 8 ignores signed overflows if
> -fno-strict-overflow of fwrapv is used.
>
> $ cat signed_overflo
On Fri, Nov 02, 2018 at 07:19:15PM +0300, Andrey Ryabinin wrote:
> UBSAN warns about signed overflows despite -fno-strict-overflow if gcc
> version is < 8. I have learned recently that UBSAN in GCC 8 ignores
> signed overflows if -fno-strict-overflow of fwrapv is used.
Ah, good.
> We can always
On 11/01/2018 07:32 PM, Peter Zijlstra wrote:
> On Thu, Nov 01, 2018 at 03:22:15PM +, Trond Myklebust wrote:
>> On Thu, 2018-11-01 at 15:59 +0100, Peter Zijlstra wrote:
>>> On Thu, Nov 01, 2018 at 01:18:46PM +, Mark Rutland wrote:
>
> My one question (and the reason why I went with
From: Paul E. McKenney
> Sent: 01 November 2018 17:02
...
> And there is a push to define C++ signed arithmetic as 2s complement,
> but there are still 1s complement systems with C compilers. Just not
> C++ compilers. Legacy...
Hmmm... I've used C compilers for DSPs where signed integer arithmet
On Fri, Nov 02, 2018 at 01:23:28PM +0100, Peter Zijlstra wrote:
> On Fri, Nov 02, 2018 at 10:56:31AM +, David Laight wrote:
> > From: Paul E. McKenney
> > > Sent: 01 November 2018 17:02
> > ...
> > > And there is a push to define C++ signed arithmetic as 2s complement,
> > > but there are still
On Fri, Nov 02, 2018 at 10:56:31AM +, David Laight wrote:
> From: Paul E. McKenney
> > Sent: 01 November 2018 17:02
> ...
> > And there is a push to define C++ signed arithmetic as 2s complement,
> > but there are still 1s complement systems with C compilers. Just not
> > C++ compilers. Legac
On Fri, Nov 02, 2018 at 10:56:31AM +, David Laight wrote:
> From: Paul E. McKenney
> > Sent: 01 November 2018 17:02
> ...
> > And there is a push to define C++ signed arithmetic as 2s complement,
> > but there are still 1s complement systems with C compilers. Just not
> > C++ compilers. Legac
On Thu, Nov 01, 2018 at 10:38:34PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 01, 2018 at 01:29:10PM -0700, Paul E. McKenney wrote:
> > On Thu, Nov 01, 2018 at 06:27:39PM +0100, Peter Zijlstra wrote:
> > > On Thu, Nov 01, 2018 at 06:14:32PM +0100, Peter Zijlstra wrote:
> > > > > This reminds me of
On Thu, Nov 01, 2018 at 06:46:50PM +0100, Dmitry Vyukov wrote:
> If there is a warning that we don't want to see at all, then we can
> disable it. It supposed to be a useful tool, rather than a thing in
> itself that lives own life. We already I think removed 1 particularly
> noisy warning and made
On Thu, Nov 01, 2018 at 01:29:10PM -0700, Paul E. McKenney wrote:
> On Thu, Nov 01, 2018 at 06:27:39PM +0100, Peter Zijlstra wrote:
> > On Thu, Nov 01, 2018 at 06:14:32PM +0100, Peter Zijlstra wrote:
> > > > This reminds me of this so silly patch :/
> > > >
> > > > https://git.kernel.org/pub/s
On Thu, Nov 01, 2018 at 06:27:39PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 01, 2018 at 06:14:32PM +0100, Peter Zijlstra wrote:
> > > This reminds me of this so silly patch :/
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=adb03115f4590baa280ddc440a
On Thu, Nov 01, 2018 at 06:14:32PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 01, 2018 at 09:59:38AM -0700, Eric Dumazet wrote:
> > On 11/01/2018 09:32 AM, Peter Zijlstra wrote:
> >
> > >> Anyhow, if the atomic maintainers are willing to stand up and state for
> > >> the record that the atomic cou
On Thu, Nov 01, 2018 at 06:18:46PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 01, 2018 at 10:01:46AM -0700, Paul E. McKenney wrote:
> > On Thu, Nov 01, 2018 at 05:32:12PM +0100, Peter Zijlstra wrote:
> > > On Thu, Nov 01, 2018 at 03:22:15PM +, Trond Myklebust wrote:
> > > > On Thu, 2018-11-01 a
On Thu, Nov 01, 2018 at 05:32:12PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 01, 2018 at 03:22:15PM +, Trond Myklebust wrote:
> > On Thu, 2018-11-01 at 15:59 +0100, Peter Zijlstra wrote:
> > > On Thu, Nov 01, 2018 at 01:18:46PM +, Mark Rutland wrote:
>
> > > > > My one question (and the r
Hi Trond,
On Thu, Nov 01, 2018 at 12:17:31AM +, Trond Myklebust wrote:
> On Wed, 2018-10-31 at 23:32 +, Paul Burton wrote:
> > In this particular case I have no idea why
> > net/sunrpc/auth_gss/gss_krb5_seal.c is using cmpxchg64() at all. It's
> > essentially reinventing atomic64_fetch_inc
On Thu, Nov 01, 2018 at 06:14:32PM +0100, Peter Zijlstra wrote:
> > This reminds me of this so silly patch :/
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=adb03115f4590baa280ddc440a8eff08a6be0cb7
You'd probably want to write it like so; +- some orderin
On Thu, Nov 01, 2018 at 10:01:46AM -0700, Paul E. McKenney wrote:
> On Thu, Nov 01, 2018 at 05:32:12PM +0100, Peter Zijlstra wrote:
> > On Thu, Nov 01, 2018 at 03:22:15PM +, Trond Myklebust wrote:
> > > On Thu, 2018-11-01 at 15:59 +0100, Peter Zijlstra wrote:
> > > > On Thu, Nov 01, 2018 at 01:
On Thu, Nov 01, 2018 at 09:59:38AM -0700, Eric Dumazet wrote:
> On 11/01/2018 09:32 AM, Peter Zijlstra wrote:
>
> >> Anyhow, if the atomic maintainers are willing to stand up and state for
> >> the record that the atomic counters are guaranteed to wrap modulo 2^n
> >> just like unsigned integers,
On 11/01/2018 09:32 AM, Peter Zijlstra wrote:
>> Anyhow, if the atomic maintainers are willing to stand up and state for
>> the record that the atomic counters are guaranteed to wrap modulo 2^n
>> just like unsigned integers, then I'm happy to take Paul's patch.
>
> I myself am certainly relyi
On Thu, Nov 01, 2018 at 03:22:15PM +, Trond Myklebust wrote:
> On Thu, 2018-11-01 at 15:59 +0100, Peter Zijlstra wrote:
> > On Thu, Nov 01, 2018 at 01:18:46PM +, Mark Rutland wrote:
> > > > My one question (and the reason why I went with cmpxchg() in the
> > > > first place) would be about
On Thu, Nov 01, 2018 at 06:30:08AM +, Trond Myklebust wrote:
[ ... ]
> >
> > For my part I agree that this would be a much better solution. The
> > argument
> > that it is not always absolutely guaranteed that atomics don't wrap
> > doesn't
> > really hold for me because it looks like they all
On Thu, 2018-11-01 at 15:59 +0100, Peter Zijlstra wrote:
> On Thu, Nov 01, 2018 at 01:18:46PM +, Mark Rutland wrote:
> > > My one question (and the reason why I went with cmpxchg() in the
> > > first
> > > place) would be about the overflow behaviour for
> > > atomic_fetch_inc() and
> > > frien
On Thu, Nov 01, 2018 at 01:18:46PM +, Mark Rutland wrote:
> > My one question (and the reason why I went with cmpxchg() in the first
> > place) would be about the overflow behaviour for atomic_fetch_inc() and
> > friends. I believe those functions should be OK on x86, so that when we
> > overfl
[adding the atomic maintainers]
On Thu, Nov 01, 2018 at 12:17:31AM +, Trond Myklebust wrote:
> On Wed, 2018-10-31 at 23:32 +, Paul Burton wrote:
> > (Copying SunRPC & net maintainers.)
> >
> > Hi Guenter,
> >
> > On Wed, Oct 31, 2018 at 03:02:53PM -0700, Guenter Roeck wrote:
> > > The al
On Wed, 2018-10-31 at 18:18 -0700, Guenter Roeck wrote:
> On 10/31/18 4:32 PM, Paul Burton wrote:
> > (Copying SunRPC & net maintainers.)
> >
> > Hi Guenter,
> >
> > On Wed, Oct 31, 2018 at 03:02:53PM -0700, Guenter Roeck wrote:
> > > The alternatives I can see are
> > > - Do not use cmpxchg64()
On 10/31/18 4:32 PM, Paul Burton wrote:
(Copying SunRPC & net maintainers.)
Hi Guenter,
On Wed, Oct 31, 2018 at 03:02:53PM -0700, Guenter Roeck wrote:
The alternatives I can see are
- Do not use cmpxchg64() outside architecture code (ie drop its use from
the offending driver, and keep doing
Hi Paul,
On Wed, 2018-10-31 at 23:32 +, Paul Burton wrote:
> (Copying SunRPC & net maintainers.)
>
> Hi Guenter,
>
> On Wed, Oct 31, 2018 at 03:02:53PM -0700, Guenter Roeck wrote:
> > The alternatives I can see are
> > - Do not use cmpxchg64() outside architecture code (ie drop its use
> > f
(Copying SunRPC & net maintainers.)
Hi Guenter,
On Wed, Oct 31, 2018 at 03:02:53PM -0700, Guenter Roeck wrote:
> The alternatives I can see are
> - Do not use cmpxchg64() outside architecture code (ie drop its use from
> the offending driver, and keep doing the same whenever the problem comes
>
On Wed, Oct 31, 2018 at 09:32:43PM +, Paul Burton wrote:
> Hi Guenter,
>
> On Wed, Oct 31, 2018 at 12:52:18PM -0700, Guenter Roeck wrote:
> > +/*
> > + * Generic version of __cmpxchg_u64, to be used for cmpxchg64().
> > + * Takes u64 parameters.
> > + */
> > +u64 __cmpxchg_u64(u64 *ptr, u64 ol
Hi Guenter,
On Wed, Oct 31, 2018 at 12:52:18PM -0700, Guenter Roeck wrote:
> +/*
> + * Generic version of __cmpxchg_u64, to be used for cmpxchg64().
> + * Takes u64 parameters.
> + */
> +u64 __cmpxchg_u64(u64 *ptr, u64 old, u64 new)
> +{
> + raw_spinlock_t *lock = lock_addr(ptr);
> + unsig
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