From: Ingo Molnar <mingo@kernel.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v2] atomic: Fix bugs in 'fetch_or()' and rename it to 'xchg_or()'
Date: Wed, 16 Mar 2016 09:14:44 +0100 [thread overview]
Message-ID: <20160316081444.GB31133@gmail.com> (raw)
In-Reply-To: <20160315170835.GA5058@lerouge>
* Frederic Weisbecker <fweisbec@gmail.com> wrote:
> > diff --git a/include/linux/atomic.h b/include/linux/atomic.h
> > index 6c502cb13c95..7bc5297bcca8 100644
> > --- a/include/linux/atomic.h
> > +++ b/include/linux/atomic.h
> > @@ -549,22 +549,28 @@ static inline int atomic_dec_if_positive(atomic_t *v)
> > #endif
> >
> > /**
> > - * fetch_or - perform *ptr |= mask and return old value of *ptr
> > - * @ptr: pointer to value
> > + * xchg_or - perform *ptr |= mask atomically and return old value of *ptr
> > + * @ptr: pointer to value (cmpxchg() compatible integer pointer type)
> > * @mask: mask to OR on the value
> > *
> > - * cmpxchg based fetch_or, macro so it works for different integer types
> > + * cmpxchg() based, it's a macro so it works for different integer types.
> > */
> > -#ifndef fetch_or
> > -#define fetch_or(ptr, mask) \
> > -({ typeof(*(ptr)) __old, __val = *(ptr); \
> > +#ifndef xchg_or
> > +# define xchg_or(ptr, mask) \
> > +({ \
> > + typeof(ptr) _ptr = (ptr); \
>
> Can we add a comment above to prevent from future mistakes with cmpxchg
> variables aliasing?
>
> I'm suprised that GCC doesn't warn about that actually.
Yeah, so in the perf tooling build we do have -Wshadow to catch such mishaps,
but not in the main kernel build.
... and yes, if I add it via the patch below the bug gets warned about:
include/linux/atomic.h:561:15: note: shadowed declaration is here
typeof(ptr) __ptr = (ptr); \
^
kernel/sched/core.c:332:11: note: in expansion of macro ‘xchg_or’
return !(xchg_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLA
... but I also get a ton of other warnings, just when building a single
kernel/sched/core.o file:
./arch/x86/include/asm/bitops.h:396:28: warning: declaration of ‘ffs’ shadows a built-in function [-Wshadow]
./arch/x86/include/asm/bitops.h:396:28: warning: declaration of ‘ffs’ shadows a built-in function [-Wshadow]
include/linux/jiffies.h:422:60: warning: declaration of ‘jiffies’ shadows a global declaration [-Wshadow]
./arch/x86/include/asm/io_apic.h:187:54: warning: declaration of ‘apic’ shadows a global declaration [-Wshadow]
./arch/x86/include/asm/bitops.h:396:28: warning: declaration of ‘ffs’ shadows a built-in function [-Wshadow]
include/linux/jiffies.h:422:60: warning: declaration of ‘jiffies’ shadows a global declaration [-Wshadow]
./arch/x86/include/asm/io_apic.h:187:54: warning: declaration of ‘apic’ shadows a global declaration [-Wshadow]
include/linux/kernel.h:750:12: warning: declaration of ‘_min1’ shadows a previous local [-Wshadow]
include/linux/kernel.h:750:12: warning: declaration of ‘_min1’ shadows a previous local [-Wshadow]
include/linux/kernel.h:751:12: warning: declaration of ‘_min2’ shadows a previous local [-Wshadow]
kernel/sched/sched.h:308:43: warning: declaration of ‘down’ shadows a global declaration [-Wshadow]
kernel/sched/sched.h:308:60: warning: declaration of ‘up’ shadows a global declaration [-Wshadow]
kernel/sched/auto_group.h:44:55: warning: declaration of ‘init_task’ shadows a global declaration [-Wshadow]
kernel/sched/core.c:635:20: warning: declaration of ‘down’ shadows a global declaration [-Wshadow]
kernel/sched/core.c:635:37: warning: declaration of ‘up’ shadows a global declaration [-Wshadow]
and yes, I'd say most of these are signatures of sloppy macros and sloppy variable
names - but it would be a ton of work to eliminate these warnings.
Thanks,
Ingo
==============>
Makefile | 3 +++
1 file changed, 3 insertions(+)
diff --git a/Makefile b/Makefile
index 7b3ecdcdc6c1..14b0ce82f2b0 100644
--- a/Makefile
+++ b/Makefile
@@ -776,6 +776,9 @@ KBUILD_CFLAGS += $(call cc-option,-Werror=date-time)
# use the deterministic mode of AR if available
KBUILD_ARFLAGS := $(call ar-option,D)
+# enforce correct pointer usage
+KBUILD_CFLAGS += $(call cc-option,-Wshadow)
+
# check for 'asm goto'
ifeq ($(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC)), y)
KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
next prev parent reply other threads:[~2016-03-16 8:15 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-14 12:32 [GIT PULL] NOHZ updates for v4.6 Ingo Molnar
2016-03-15 2:44 ` Linus Torvalds
2016-03-15 8:42 ` Peter Zijlstra
2016-03-15 9:49 ` Ingo Molnar
2016-03-15 9:32 ` [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to 'xchg_or()' Ingo Molnar
2016-03-15 10:50 ` Peter Zijlstra
2016-03-15 12:08 ` Ingo Molnar
2016-03-15 12:42 ` Peter Zijlstra
2016-03-15 11:06 ` Peter Zijlstra
2016-03-15 11:59 ` Peter Zijlstra
2016-03-15 12:01 ` Ingo Molnar
2016-03-15 12:32 ` Ingo Molnar
2016-03-15 12:37 ` Ingo Molnar
2016-03-15 13:17 ` Peter Zijlstra
2016-03-15 12:21 ` [PATCH v2] " Ingo Molnar
2016-03-15 13:26 ` Peter Zijlstra
2016-03-16 8:04 ` Ingo Molnar
2016-03-16 8:29 ` Peter Zijlstra
2016-03-15 17:08 ` Frederic Weisbecker
2016-03-16 8:14 ` Ingo Molnar [this message]
2016-03-17 0:54 ` Frederic Weisbecker
2016-03-15 16:18 ` [PATCH] " Linus Torvalds
2016-03-15 9:53 ` [PATCH] nohz: Change tick_dep_mask from 'unsigned long' to 'unsigned int' Ingo Molnar
2016-03-15 12:15 ` Ingo Molnar
2016-03-15 16:30 ` Linus Torvalds
2016-03-15 17:28 ` Frederic Weisbecker
2016-03-15 17:36 ` Linus Torvalds
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