From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from canpmsgout09.his.huawei.com (canpmsgout09.his.huawei.com [113.46.200.224]) (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 BE2B43B1EEE; Fri, 4 Sep 2026 07:32:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.224 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788507150; cv=none; b=vEvNKH+8WcQh1SWPkI/Jt9lC38aKk5JFnLFa0JEs4cvQwBYvFFKywBha51aplw/gii+J8RxOfVZ8MZexSHUfdaTFEMGl3DXEew5l9WrRtAxSnfkjVR7mRhc75Usu17ebBOaItHEfyedCNP8Ia7CQT6kYANUW/qaLHroOCQNP+lY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788507150; c=relaxed/simple; bh=xOY2Lm5YDkZICkADu3TwD0cD3gJDODMdk993CAsAPQ0=; h=From:To:CC:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Oa4aL+xFgJwkW49gb+A2UVmJz5hFoI8a+Kx7WalsugQySHGU7kN9a/WE3H6izY0AsIRXGCXJMbFZ6cNBE6zAmO89sA5t2jHcjeN5zzOrenVczcnDUtz0bfbtARfsjIdqwgPJKmWYrRSDSZkaFM1pW7Tu6HfYNkH1y4Cv8uveVug= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=32AVeswh; arc=none smtp.client-ip=113.46.200.224 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="32AVeswh" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=HLDguLzm9iebYGNiy9mxz1ksVC/JrRbR0DUr/nUScuY=; b=32AVeswhGrDouEzpIpM10Fwh1TltViA2siahd/ovMCl2bgTFZYk6A814vPb0uQFV7Mu1hdJU8 Dsb0XilvJRglEXM/RIj2RMtn56wWzbIayLTDPFkdBXOpdsG5Vti5kkqTXEEjhleW8SiJ2UTL8g5 3021/Wcjx0YcbP7maBIFW4M= Received: from mail.maildlp.com (unknown [172.19.163.214]) by canpmsgout09.his.huawei.com (SkyGuard) with ESMTPS id 4hbnvL0knZz1cyVg; Fri, 4 Sep 2026 15:21:18 +0800 (CST) Received: from kwepemk200008.china.huawei.com (unknown [7.202.194.74]) by mail.maildlp.com (Postfix) with ESMTPS id 9FDCF4056C; Fri, 4 Sep 2026 15:32:08 +0800 (CST) Received: from huawei.com (10.90.53.73) by kwepemk200008.china.huawei.com (7.202.194.74) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.45; Fri, 4 Sep 2026 15:32:07 +0800 From: Jinjie Ruan To: , , , , , , , , CC: Subject: [PATCH v4 2/2] ext4: Convert group-count barrier protocol to acquire/release Date: Fri, 4 Sep 2026 15:32:53 +0800 Message-ID: <20260904073253.663243-3-ruanjinjie@huawei.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260904073253.663243-1-ruanjinjie@huawei.com> References: <20260904073253.663243-1-ruanjinjie@huawei.com> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: kwepems200001.china.huawei.com (7.221.188.67) To kwepemk200008.china.huawei.com (7.202.194.74) During an online resize, reading s_groups_count and s_blockfile_groups requires strict ordering against subsequent initialized block group metadata. Replace the historical smp_wmb()/smp_rmb() pairs with smp_store_release() and smp_load_acquire(). This formalizes the publish-subscribe pattern and allows weakly-ordered architectures (e.g., arm64) to utilize native STLR/LDAR instructions instead of full DMB fences. Update the documentation in resize.c and ext4.h accordingly. Assisted-by: Gemini:Gemini-3.1 Assisted-by: DeepSeek:DeepSeek-V3 Reviewed-by: Zhang Yi Reviewed-by: Jan Kara Signed-off-by: Jinjie Ruan --- Cc: Theodore Ts'o Cc: Andreas Dilger Cc: Baokun Li Cc: Jan Kara Cc: Ojaswin Mujoo Cc: Ritesh Harjani (IBM) Cc: Zhang Yi --- fs/ext4/ext4.h | 10 +++------- fs/ext4/mballoc.c | 6 ++---- fs/ext4/resize.c | 19 +++++++++++-------- 3 files changed, 16 insertions(+), 19 deletions(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 724a27e8be61..d70b9cb09155 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -3542,16 +3542,12 @@ static inline void ext4_isize_set(struct ext4_inode *raw_inode, loff_t i_size) } /* - * Reading s_groups_count requires using smp_rmb() afterwards. See - * the locking protocol documented in the comments of ext4_group_add() - * in resize.c + * Reading s_groups_count uses acquire semantics. */ static inline ext4_group_t ext4_get_groups_count(struct super_block *sb) { - ext4_group_t ngroups = EXT4_SB(sb)->s_groups_count; - - smp_rmb(); - return ngroups; + /* Pairs with smp_store_release() in ext4_update_super() */ + return smp_load_acquire(&EXT4_SB(sb)->s_groups_count); } static inline ext4_group_t ext4_flex_group(struct ext4_sb_info *sbi, diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 06171a11db12..a15285224cdf 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -899,10 +899,8 @@ static ext4_group_t ext4_get_allocation_groups_count( /* non-extent files are limited to low blocks/groups */ if (!(ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS))) - ngroups = EXT4_SB(ac->ac_sb)->s_blockfile_groups; - - /* Pairs with smp_wmb() in ext4_update_super() */ - smp_rmb(); + /* Pairs with smp_store_release() in ext4_update_super() */ + ngroups = smp_load_acquire(&EXT4_SB(ac->ac_sb)->s_blockfile_groups); return ngroups; } diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c index 2c5b851c552a..5e3ad8393cf8 100644 --- a/fs/ext4/resize.c +++ b/fs/ext4/resize.c @@ -1462,11 +1462,11 @@ static void ext4_update_super(struct super_block *sb, * * The precise rules we use are: * - * * Writers must perform a smp_wmb() after updating all - * dependent data and before modifying the groups count + * * Writers must use a release store when updating the groups count + * after all dependent data has been updated * - * * Readers must perform an smp_rmb() after reading the groups - * count and before reading any dependent data. + * * Readers must use an acquire load when reading the groups + * count before reading any dependent data. * * NB. These rules can be relaxed when checking the group count * while freeing data, as we can only allocate from a block @@ -1474,12 +1474,15 @@ static void ext4_update_super(struct super_block *sb, * only then free after serialising in turn against that * allocation. */ - smp_wmb(); /* Update the global fs size fields */ - sbi->s_groups_count += flex_gd->count; - sbi->s_blockfile_groups = min(sbi->s_groups_count, - (EXT4_MAX_BLOCK_FILE_PHYS / EXT4_BLOCKS_PER_GROUP(sb))); + /* Pairs with smp_load_acquire() in ext4_get_groups_count() */ + smp_store_release(&sbi->s_groups_count, + sbi->s_groups_count + flex_gd->count); + /* Pairs with smp_load_acquire() in ext4_get_allocation_groups_count() */ + smp_store_release(&sbi->s_blockfile_groups, + min(sbi->s_groups_count, + (EXT4_MAX_BLOCK_FILE_PHYS / EXT4_BLOCKS_PER_GROUP(sb)))); /* Update the reserved block counts only once the new group is * active. */ -- 2.34.1