From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: Arnd Bergmann <arnd@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Matthew Wilcox <willy@infradead.org>,
Ingo Molnar <mingo@kernel.org>, Will Deacon <will@kernel.org>,
Will Deacon <will.deacon@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Nicholas Piggin <npiggin@gmail.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Herbert Xu <herbert@gondor.apana.org.au>,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] qspinlock: use signed temporaries for cmpxchg
Date: Tue, 27 Oct 2020 08:47:26 +0100 [thread overview]
Message-ID: <20201027074726.GX2611@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <022365e9-f7fe-5589-7867-d2ad2d33cfa3@redhat.com>
On Mon, Oct 26, 2020 at 02:03:06PM -0400, Waiman Long wrote:
> On 10/26/20 12:57 PM, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > When building with W=2, the build log is flooded with
> >
> > include/asm-generic/qrwlock.h:65:56: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
> > include/asm-generic/qrwlock.h:92:53: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
> > include/asm-generic/qspinlock.h:68:55: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
> > include/asm-generic/qspinlock.h:82:52: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
> >
> > The atomics are built on top of signed integers, but the caller
> > doesn't actually care. Just use signed types as well.
Code consistency cares. Fundamentally we're treating it as a u32 here,
using int just because of a confused compiler warning will confuse.
> > @@ -77,7 +77,7 @@ extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
> > */
> > static __always_inline void queued_spin_lock(struct qspinlock *lock)
> > {
> > - u32 val = 0;
> > + int val = 0;
> > if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL)))
> > return;
> Yes, it shouldn't really matter if the value is defined as int or u32.
> However, the only caveat that I see is queued_spin_lock_slowpath() is
> expecting a u32 argument. Maybe you should cast it back to (u32) when
> calling it.
No, we're not going to confuse the code. That stuff is hard enough as it
is. This warning is garbage and just needs to stay off.
next prev parent reply other threads:[~2020-10-27 7:47 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-26 16:57 [PATCH] qspinlock: use signed temporaries for cmpxchg Arnd Bergmann
2020-10-26 17:10 ` Peter Zijlstra
2020-10-26 18:03 ` Waiman Long
2020-10-27 7:47 ` Peter Zijlstra [this message]
2020-10-27 8:33 ` Arnd Bergmann
2020-10-27 10:32 ` Peter Zijlstra
2020-10-27 13:38 ` David Laight
2020-10-27 16:22 ` Arnd Bergmann
2020-10-27 17:34 ` Peter Zijlstra
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20201027074726.GX2611@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=arnd@arndb.de \
--cc=arnd@kernel.org \
--cc=herbert@gondor.apana.org.au \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=longman@redhat.com \
--cc=mingo@kernel.org \
--cc=mpe@ellerman.id.au \
--cc=npiggin@gmail.com \
--cc=tglx@linutronix.de \
--cc=will.deacon@arm.com \
--cc=will@kernel.org \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).