From: Philipp Stanner <phasta@mailbox.org>
To: "Gary Guo" <gary@garyguo.net>,
phasta@kernel.org, "Sumit Semwal" <sumit.semwal@linaro.org>,
"Christian König" <christian.koenig@amd.com>,
"Yury Norov" <yury.norov@gmail.com>,
"Rasmus Villemoes" <linux@rasmusvillemoes.dk>,
"Arnd Bergmann" <arnd@arndb.de>,
"Tvrtko Ursulin" <tvrtko.ursulin@igalia.com>,
"Danilo Krummrich" <dakr@kernel.org>,
"Paul E . McKenney" <paulmck@kernel.org>
Cc: linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: [PATCH 1/2] asm-generic/bitops: Add set_bit_release()
Date: Wed, 21 Oct 2026 15:22:54 +0200 [thread overview]
Message-ID: <d305166f022bd567cb03f8fb5c8b9f2aa9e6b5fd.camel@mailbox.org> (raw)
In-Reply-To: <DMAIIIJ57A3N.GXLM3L5IOAPL@garyguo.net>
On Wed, 2026-10-21 at 13:24 +0100, Gary Guo wrote:
> On Wed Oct 21, 2026 at 1:17 PM BST, Philipp Stanner wrote:
[…]
> > static __always_inline bool test_and_set_bit(long nr, volatile unsigned long *addr)
> > {
> > kcsan_mb();
> > instrument_atomic_read_write(addr + BIT_WORD(nr), sizeof(long));
> > return arch_test_and_set_bit(nr, addr);
> > }
> >
> > Where does the "full ordering" come from? I suppose implied barrier
> > then means it comes from the architecture's implementation. But what's
> > then the purpose of kcsan_XX ?
>
> It's from arch_test_and_set_bit.
>
> KCSAN doesn't see arch code, so the kcsan_mb() and in fact
> instrumnent_atomic_read_write() both are annotations to indicate that this is
> conceptually a mb() + STORE for instrumentation purpose.
We (i.e., someone who's got the overview) could probably document where
and why our atomic instructions are a bit scattered.
Why is test_bit_acquire() defined in include/linux/bitops.h, and should
set_bit_release() be defined there – or here?
P.
next prev parent reply other threads:[~2026-10-21 13:23 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-21 9:55 [PATCH 0/2] dma-fence: Order is-signaled-bit Philipp Stanner
2026-10-21 9:55 ` [PATCH 1/2] asm-generic/bitops: Add set_bit_release() Philipp Stanner
2026-10-21 11:33 ` Arnd Bergmann
2026-10-21 11:54 ` Gary Guo
2026-10-21 12:15 ` Arnd Bergmann
2026-10-21 12:06 ` Gary Guo
2026-10-21 12:17 ` Philipp Stanner
2026-10-21 12:24 ` Gary Guo
2026-10-21 13:22 ` Philipp Stanner [this message]
2026-10-21 9:55 ` [PATCH 2/2] dma-buf/dma-fence: Order setting of the signaled-bit properly Philipp Stanner
2026-10-21 13:47 ` Christian König
2026-10-21 14:52 ` Philipp Stanner
2026-10-21 15:04 ` Christian König
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