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 E7D4A634E1; Tue, 16 Jan 2024 00:28:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="g9S8aGIR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E5F5BC433C7; Tue, 16 Jan 2024 00:28:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1705364919; bh=NrbAoz5+i9g+hKypIOHJbUt6vp+WfHfF6+UtqbL4uq0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=g9S8aGIRWDw7SK+Yu1aWnpWMi1+w2L7jFic3k6c5egKNDVNdkXovoCeuH0bkFXJ4r 6nSAQlIxOeGKuk5FJ0wcU+80HEn9Bfw8sdBxhmuN/HyLHY2+8MJ3JVReGPTdG1XjrQ Xckyrq9+zxFtwMo4/ta3pJZDSLv3iW4lezt1CFOQ3I4lx+AaKZNCESG3ouuCjznziS LAq/Os04lK4EvETNjGrFpl8ooWO3tXzQnG9fnEfa8wHGVQ9aDglqY8fsu4Lbq/gddx tz2naQENEn3nDNgK022zYYxFqcg09oALfq8IafytdprPn4TkzJS+tY0Tg9fbL25lQC /gJDxah4TVTdA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Oleg Nesterov , David Howells , Marc Dionne , linux-afs@lists.infradead.org, Sasha Levin Subject: [PATCH AUTOSEL 4.19 09/12] afs: fix the usage of read_seqbegin_or_lock() in afs_find_server*() Date: Mon, 15 Jan 2024 19:28:02 -0500 Message-ID: <20240116002817.216837-9-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240116002817.216837-1-sashal@kernel.org> References: <20240116002817.216837-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 4.19.305 Content-Transfer-Encoding: 8bit From: Oleg Nesterov [ Upstream commit 1702e0654ca9a7bcd7c7619c8a5004db58945b71 ] David Howells says: (5) afs_find_server(). There could be a lot of servers in the list and each server can have multiple addresses, so I think this would be better with an exclusive second pass. The server list isn't likely to change all that often, but when it does change, there's a good chance several servers are going to be added/removed one after the other. Further, this is only going to be used for incoming cache management/callback requests from the server, which hopefully aren't going to happen too often - but it is remotely drivable. (6) afs_find_server_by_uuid(). Similarly to (5), there could be a lot of servers to search through, but they are in a tree not a flat list, so it should be faster to process. Again, it's not likely to change that often and, again, when it does change it's likely to involve multiple changes. This can be driven remotely by an incoming cache management request but is mostly going to be driven by setting up or reconfiguring a volume's server list - something that also isn't likely to happen often. Make the "seq" counter odd on the 2nd pass, otherwise read_seqbegin_or_lock() never takes the lock. Signed-off-by: Oleg Nesterov Signed-off-by: David Howells cc: Marc Dionne cc: linux-afs@lists.infradead.org Link: https://lore.kernel.org/r/20231130115614.GA21581@redhat.com/ Signed-off-by: Sasha Levin --- fs/afs/server.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/fs/afs/server.c b/fs/afs/server.c index 2c7f6211c360..b12caa1acf53 100644 --- a/fs/afs/server.c +++ b/fs/afs/server.c @@ -37,7 +37,7 @@ struct afs_server *afs_find_server(struct afs_net *net, const struct afs_addr_list *alist; struct afs_server *server = NULL; unsigned int i; - int seq = 0, diff; + int seq = 1, diff; rcu_read_lock(); @@ -45,6 +45,7 @@ struct afs_server *afs_find_server(struct afs_net *net, if (server) afs_put_server(net, server); server = NULL; + seq++; /* 2 on the 1st/lockless path, otherwise odd */ read_seqbegin_or_lock(&net->fs_addr_lock, &seq); if (srx->transport.family == AF_INET6) { @@ -100,7 +101,7 @@ struct afs_server *afs_find_server_by_uuid(struct afs_net *net, const uuid_t *uu { struct afs_server *server = NULL; struct rb_node *p; - int diff, seq = 0; + int diff, seq = 1; _enter("%pU", uuid); @@ -112,7 +113,7 @@ struct afs_server *afs_find_server_by_uuid(struct afs_net *net, const uuid_t *uu if (server) afs_put_server(net, server); server = NULL; - + seq++; /* 2 on the 1st/lockless path, otherwise odd */ read_seqbegin_or_lock(&net->fs_lock, &seq); p = net->fs_servers.rb_node; -- 2.43.0