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From: "Arnd Bergmann" <arnd@arndb.de>
To: "Gary Guo" <gary@garyguo.net>,
	"Philipp Stanner" <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>,
	"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 <linux-arch@vger.kernel.org>
Subject: Re: [PATCH 1/2] asm-generic/bitops: Add set_bit_release()
Date: Wed, 21 Oct 2026 14:15:56 +0200	[thread overview]
Message-ID: <9505cbc2-7261-4f84-9769-b97e9acb1c38@app.fastmail.com> (raw)
In-Reply-To: <DMAHVQLCMQAN.3G0TBMA1UTM6H@garyguo.net>

On Wed, Oct 21, 2026, at 13:54, Gary Guo wrote:
> On Wed Oct 21, 2026 at 12:33 PM BST, Arnd Bergmann wrote:

>> I'm always confused by this and the new function makes it harder
>> to understand in the current form:
...
>> - Contrary to that, the kerneldoc comment over set_bit() mentions
>>   "This is a relaxed atomic operation (no implied memory barriers)"
>>   and leaves out the kcsan_mb() that is in test_and_set_bit().
>>   This makes the new set_bit_release() sound like a /stronger/
>>   version of set_bit() the same way that test_bit_acquire()
>>   is a stronger version of the (relaxed) test_bit().
>
> set_bit has relaxed semantics while test_and_set_bit implies barrier. RISC-V for
> exmaple will generate the amoor instruction for set_bit, not amoor.aqrl.

Thanks for the clarification, I did misread the implementation
and see how I was confused once more.

     Arnd

  reply	other threads:[~2026-10-21 12:16 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 [this message]
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
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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