From nobody Sun Nov 24 06:36:02 2024 Received: from szxga07-in.huawei.com (szxga07-in.huawei.com [45.249.212.35]) (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 93E871F6680; Thu, 7 Nov 2024 11:10:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.35 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730977836; cv=none; b=skrWbP9bOkTrms3YwgNDaK6c9krYyofrTVWOplqQuelKk+USM2FwP37mOpdTcCgTxYIux7FxvA/lBIaUZyHnTGtdDYkNqRFp32iRTVIjqxAxfTTgZnu7rWHyHwiDWSFgMJ2kCpRBeXpoOhZrAoUcaoVVufrojD2IQAeoIHgk3kI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730977836; c=relaxed/simple; bh=qWDhbIEFWCOCwM370sGSBoKdqofWiHM85gaoBK1VQNk=; h=From:To:CC:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=fG5gELsDnbohBGPbxpG3B0U0NI6kMdJl+z7EesX022yI7r/9qbK94rG2WRf2En8DI84aoHB8RhyzGaETrJ8VUcJQDq4PIFIEyJsUOEU9EQmRE8ADXeOYdQsk4zEBWxD7l9GoHcJxswDBRu8ppgsF2hKGhmTOPVQEUz1jy9U1Gtw= 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; arc=none smtp.client-ip=45.249.212.35 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 Received: from mail.maildlp.com (unknown [172.19.163.17]) by szxga07-in.huawei.com (SkyGuard) with ESMTP id 4XkfT7637Rz1SGC6; Thu, 7 Nov 2024 19:08:43 +0800 (CST) Received: from kwepemf100017.china.huawei.com (unknown [7.202.181.16]) by mail.maildlp.com (Postfix) with ESMTPS id C45F41A0188; Thu, 7 Nov 2024 19:10:26 +0800 (CST) Received: from huawei.com (10.175.104.67) by kwepemf100017.china.huawei.com (7.202.181.16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Thu, 7 Nov 2024 19:10:25 +0800 From: Zizhi Wo To: , , , CC: , , , , , , , , , , Subject: [PATCH v2 5/5] netfs/fscache: Add a memory barrier for FSCACHE_VOLUME_CREATING Date: Thu, 7 Nov 2024 19:06:49 +0800 Message-ID: <20241107110649.3980193-6-wozizhi@huawei.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20241107110649.3980193-1-wozizhi@huawei.com> References: <20241107110649.3980193-1-wozizhi@huawei.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To kwepemf100017.china.huawei.com (7.202.181.16) Content-Type: text/plain; charset="utf-8" In fscache_create_volume(), there is a missing memory barrier between the bit-clearing operation and the wake-up operation. This may cause a situation where, after a wake-up, the bit-clearing operation hasn't been detected yet, leading to an indefinite wait. The triggering process is as follows: [cookie1] [cookie2] [volume_work] fscache_perform_lookup fscache_create_volume fscache_perform_lookup fscache_create_volume fscache_create_volume_work cachefiles_acquire_volume clear_and_wake_up_bit test_and_set_bit test_and_set_bit goto maybe_wait goto no_wait In the above process, cookie1 and cookie2 has the same volume. When cookie1 enters the -no_wait- process, it will clear the bit and wake up the waiting process. If a barrier is missing, it may cause cookie2 to remain in the -wait- process indefinitely. In commit 3288666c7256 ("fscache: Use clear_and_wake_up_bit() in fscache_create_volume_work()"), barriers were added to similar operations in fscache_create_volume_work(), but fscache_create_volume() was missed. By combining the clear and wake operations into clear_and_wake_up_bit() to fix this issue. Fixes: bfa22da3ed65 ("fscache: Provide and use cache methods to lookup/crea= te/free a volume") Signed-off-by: Zizhi Wo Acked-by: David Howells --- fs/netfs/fscache_volume.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/fs/netfs/fscache_volume.c b/fs/netfs/fscache_volume.c index cb75c07b5281..ced14ac78cc1 100644 --- a/fs/netfs/fscache_volume.c +++ b/fs/netfs/fscache_volume.c @@ -322,8 +322,7 @@ void fscache_create_volume(struct fscache_volume *volum= e, bool wait) } return; no_wait: - clear_bit_unlock(FSCACHE_VOLUME_CREATING, &volume->flags); - wake_up_bit(&volume->flags, FSCACHE_VOLUME_CREATING); + clear_and_wake_up_bit(FSCACHE_VOLUME_CREATING, &volume->flags); } =20 /* --=20 2.39.2