From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 37F7A3F9D2; Tue, 12 Aug 2025 18:03:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755021806; cv=none; b=Vfmi8OKr8K80ubI1O9EArOj5bwD8eMhDma8WxMRK8TgqWaHxNp9dZ46rp78Oy1INHoeooNHG7drmNXyq8dsq+XNbEJ2sQbkIuAydKWEmxXQgwUAhh4eulCzO5zlxH1IEOEu7Nir4yW0NjWygBBqQ0eMLvH2OzgU/gJ4mxeJSylI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755021806; c=relaxed/simple; bh=pkfVsCwkiEn7BS+q1YNCI8XDaX4qBppjVIhIvTLnoKc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=A8A39KlbmOcSb5JinExOfoKCf8BCJNQb2CeRFkxDkPlTLgK7+kt1aslk5YTCwJe5b0CzVV799RXyrK1LSzOEpdqqm8nwWlkQaaQvBNutBQpoaldJPKHMg2wLbUBe5LbHKrQqHHm62SEv8Vk5Zrg8uLXTzmawBPj7LRBo+FXAjvw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=iJ9y+Qm4; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="iJ9y+Qm4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B119BC4CEF6; Tue, 12 Aug 2025 18:03:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1755021806; bh=pkfVsCwkiEn7BS+q1YNCI8XDaX4qBppjVIhIvTLnoKc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iJ9y+Qm4GgGVSl7sb1qBLV1rrrdbC7Icbfoa0ylc5vAVLspkeGj0GsJQyjqkJkf+a rglsD0Z5+oRdYTAuqheLIEj3A4U+ia2xN5UoKLJkApuVPTNRE/EVFSFZhFzqc8bDnw ALN1gXxP29tNbiFtsCsjTeW+CCyiUlM7YFrDSM7Q= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, NeilBrown , "Peter Zijlstra (Intel)" , Sasha Levin Subject: [PATCH 6.6 197/262] sched: Add test_and_clear_wake_up_bit() and atomic_dec_and_wake_up() Date: Tue, 12 Aug 2025 19:29:45 +0200 Message-ID: <20250812173001.547247650@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250812172952.959106058@linuxfoundation.org> References: <20250812172952.959106058@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: NeilBrown [ Upstream commit 52d633def56c10fe3e82a2c5d88c3ecb3f4e4852 ] There are common patterns in the kernel of using test_and_clear_bit() before wake_up_bit(), and atomic_dec_and_test() before wake_up_var(). These combinations don't need extra barriers but sometimes include them unnecessarily. To help avoid the unnecessary barriers and to help discourage the general use of wake_up_bit/var (which is a fragile interface) introduce two combined functions which implement these patterns. Also add store_release_wake_up() which supports the task of simply setting a non-atomic variable and sending a wakeup. This pattern requires barriers which are often omitted. Signed-off-by: NeilBrown Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20240925053405.3960701-5-neilb@suse.de Stable-dep-of: 1db3a48e83bb ("NFS: Fix wakeup of __nfs_lookup_revalidate() in unblock_revalidate()") Signed-off-by: Sasha Levin --- include/linux/wait_bit.h | 60 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 60 insertions(+) diff --git a/include/linux/wait_bit.h b/include/linux/wait_bit.h index 7725b7579b78..2209c227e859 100644 --- a/include/linux/wait_bit.h +++ b/include/linux/wait_bit.h @@ -335,4 +335,64 @@ static inline void clear_and_wake_up_bit(int bit, void *word) wake_up_bit(word, bit); } +/** + * test_and_clear_wake_up_bit - clear a bit if it was set: wake up anyone waiting on that bit + * @bit: the bit of the word being waited on + * @word: the address of memory containing that bit + * + * If the bit is set and can be atomically cleared, any tasks waiting in + * wait_on_bit() or similar will be woken. This call has the same + * complete ordering semantics as test_and_clear_bit(). Any changes to + * memory made before this call are guaranteed to be visible after the + * corresponding wait_on_bit() completes. + * + * Returns %true if the bit was successfully set and the wake up was sent. + */ +static inline bool test_and_clear_wake_up_bit(int bit, unsigned long *word) +{ + if (!test_and_clear_bit(bit, word)) + return false; + /* no extra barrier required */ + wake_up_bit(word, bit); + return true; +} + +/** + * atomic_dec_and_wake_up - decrement an atomic_t and if zero, wake up waiters + * @var: the variable to dec and test + * + * Decrements the atomic variable and if it reaches zero, send a wake_up to any + * processes waiting on the variable. + * + * This function has the same complete ordering semantics as atomic_dec_and_test. + * + * Returns %true is the variable reaches zero and the wake up was sent. + */ + +static inline bool atomic_dec_and_wake_up(atomic_t *var) +{ + if (!atomic_dec_and_test(var)) + return false; + /* No extra barrier required */ + wake_up_var(var); + return true; +} + +/** + * store_release_wake_up - update a variable and send a wake_up + * @var: the address of the variable to be updated and woken + * @val: the value to store in the variable. + * + * Store the given value in the variable send a wake up to any tasks + * waiting on the variable. All necessary barriers are included to ensure + * the task calling wait_var_event() sees the new value and all values + * written to memory before this call. + */ +#define store_release_wake_up(var, val) \ +do { \ + smp_store_release(var, val); \ + smp_mb(); \ + wake_up_var(var); \ +} while (0) + #endif /* _LINUX_WAIT_BIT_H */ -- 2.39.5