From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Ro8tuo5Y" Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 80C2EB2 for ; Wed, 13 Dec 2023 05:50:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1702475413; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ExN3aXWl+sIeMUeAn84eZ7A4PvMHoy42dD/Wo7lzJak=; b=Ro8tuo5Y6TxBFIVsVjZPSsKqPyleOoColEjqudPxKL02eiSgTT6FvW8FH2VtQr/9D8mjZs QAx067pSoAJWgPzkwsJtwMum7FIxqR4DjpFVkg+EuTAilRpUA4E4y2mb+q6qRWIf4+dF8T JgWRZ/+fnvxOWRYEAF96EX55491FFFE= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-627-lg-8yNpGM3GXbqS7N0i_IQ-1; Wed, 13 Dec 2023 08:50:10 -0500 X-MC-Unique: lg-8yNpGM3GXbqS7N0i_IQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 13EAE83718B; Wed, 13 Dec 2023 13:50:10 +0000 (UTC) Received: from warthog.procyon.org.com (unknown [10.42.28.2]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2723840C6EBA; Wed, 13 Dec 2023 13:50:09 +0000 (UTC) From: David Howells To: Marc Dionne Cc: David Howells , linux-afs@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Oleg Nesterov Subject: [PATCH v2 02/40] afs: fix the usage of read_seqbegin_or_lock() in afs_find_server*() Date: Wed, 13 Dec 2023 13:49:24 +0000 Message-ID: <20231213135003.367397-3-dhowells@redhat.com> In-Reply-To: <20231213135003.367397-1-dhowells@redhat.com> References: <20231213135003.367397-1-dhowells@redhat.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.2 From: Oleg Nesterov 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/ --- 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 b5237206eac3..0bd2f5ba6900 100644 --- a/fs/afs/server.c +++ b/fs/afs/server.c @@ -27,7 +27,7 @@ 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(); @@ -35,6 +35,7 @@ struct afs_server *afs_find_server(struct afs_net *net, if (server) afs_unuse_server_notime(net, server, afs_server_trace_put_find_rsq); 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) { @@ -90,7 +91,7 @@ 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); @@ -102,7 +103,7 @@ struct afs_server *afs_find_server_by_uuid(struct afs_net *net, const uuid_t *uu if (server) afs_unuse_server(net, server, afs_server_trace_put_uuid_rsq); 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;