From: Mark Rutland <mark.rutland@arm.com>
To: Marco Elver <elver@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Boqun Feng <boqun.feng@gmail.com>, Borislav Petkov <bp@alien8.de>,
Catalin Marinas <catalin.marinas@arm.com>,
Dmitry Vyukov <dvyukov@google.com>,
Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
jonas@southpole.se, juri.lelli@redhat.com,
Russell King - ARM Linux admin <linux@armlinux.org.uk>,
Andy Lutomirski <luto@kernel.org>,
Matt Turner <mattst88@gmail.com>, Ingo Molnar <mingo@redhat.com>,
Michal Simek <monstr@monstr.eu>,
Michael Ellerman <mpe@ellerman.id.au>,
"Paul E. McKenney" <paulmck@kernel.org>,
Paul Mackerras <paulus@samba.org>,
Peter Zijlstra <peterz@infradead.org>,
Richard Henderson <rth@twiddle.net>,
shorne@gmail.com, stefan.kristiansson@saunalahti.fi,
Thomas Gleixner <tglx@linutronix.de>,
vincent.guittot@linaro.org, Will Deacon <will@kernel.org>
Subject: Re: [RFC PATCH 01/10] thread_info: add helpers to snapshot thread flags
Date: Fri, 11 Jun 2021 10:17:24 +0100 [thread overview]
Message-ID: <20210611091724.GA78056@C02TD0UTHF1T.local> (raw)
In-Reply-To: <CANpmjNOvnqE29mMU++K0VMibF8xMixJXRDqbDKXjXuxobAfM1Q@mail.gmail.com>
On Thu, Jun 10, 2021 at 11:01:34AM +0200, Marco Elver wrote:
> On Wed, 9 Jun 2021 at 14:20, Mark Rutland <mark.rutland@arm.com> wrote:
> >
> > We have common helpers to manipulate individual thread flags, but where
> > code wants to check several flags at once, it must open code reading
> > current_thread_info()->flags and operating on a snapshot.
> >
> > As some flags can be set remotely it's necessary to use READ_ONCE() to
> > get a consistent snapshot even when IRQs are disabled, but some code
> > forgets to do this. Generally this is unlike to cause a problem in
> > practice, but it is somewhat unsound, and KCSAN will legitimately warn
> > that there is a data race.
> >
> > To make it easier to do the right thing, and to highlight that
> > concurrent modification is possible, let's add a new helpers to snapshot
> > the flags, which should be used in preference to plain reads.
> > Subsequent patches will move existing code to use the new helpers.
> >
> > Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> > Cc: Boqun Feng <boqun.feng@gmail.com>
> > Cc: Dmitry Vyukov <dvyukov@google.com>
> > Cc: Marco Elver <elver@google.com>
> > Cc: Paul E. McKenney <paulmck@kernel.org>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Will Deacon <will@kernel.org>
>
> Acked-by: Marco Elver <elver@google.com>
Thanks!
> > ---
> > include/linux/thread_info.h | 10 ++++++++++
> > 1 file changed, 10 insertions(+)
> >
> > diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
> > index 157762db9d4b..f3769842046d 100644
> > --- a/include/linux/thread_info.h
> > +++ b/include/linux/thread_info.h
> > @@ -117,6 +117,11 @@ static inline int test_ti_thread_flag(struct thread_info *ti, int flag)
> > return test_bit(flag, (unsigned long *)&ti->flags);
> > }
> >
> > +static inline unsigned long read_ti_thread_flags(struct thread_info *ti)
> > +{
> > + return READ_ONCE(ti->flags);
> > +}
> > +
>
> Are some of the callers 'noinstr'? I haven't seen it in this series
> yet, but if yes, then not inlining (which some compilers may do with
> heavier instrumentation) might cause issues and this could be
> __always_inline.
That's a very good point; I agree it should be __always_inline, and I'll
fix that up for the next spin.
Thanks,
Mark.
next prev parent reply other threads:[~2021-06-11 9:17 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-09 12:19 [RFC PATCH 00/10] thread_info: use helpers to snapshot thread flags Mark Rutland
2021-06-09 12:19 ` [RFC PATCH 01/10] thread_info: add " Mark Rutland
2021-06-10 9:01 ` Marco Elver
2021-06-11 9:17 ` Mark Rutland [this message]
2021-06-19 22:28 ` Thomas Gleixner
2021-06-21 8:29 ` Mark Rutland
2021-06-09 12:19 ` [RFC PATCH 02/10] entry: " Mark Rutland
2021-06-09 12:19 ` [RFC PATCH 03/10] sched: " Mark Rutland
2021-06-09 12:19 ` [RFC PATCH 04/10] alpha: " Mark Rutland
2021-06-09 12:19 ` [RFC PATCH 05/10] arm: " Mark Rutland
2021-06-09 12:19 ` [RFC PATCH 06/10] arm64: read " Mark Rutland
2021-06-09 12:19 ` [RFC PATCH 07/10] microblaze: snapshot " Mark Rutland
2021-06-09 12:19 ` [RFC PATCH 08/10] openrisc: " Mark Rutland
2021-06-10 19:14 ` Stafford Horne
2021-06-09 12:20 ` [RFC PATCH 09/10] powerpc: " Mark Rutland
2021-06-15 13:18 ` Michael Ellerman
2021-06-21 8:46 ` Mark Rutland
2021-06-09 12:20 ` [RFC PATCH 10/10] x86: " Mark Rutland
2021-06-19 22:30 ` Thomas Gleixner
2021-06-21 8:35 ` Mark Rutland
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