From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Elder Subject: [PATCH 2/4] ceph: kill addr_str_lock spinlock; use atomic instead Date: Tue, 28 Feb 2012 19:12:12 -0800 Message-ID: <4F4D978C.7090704@dreamhost.com> References: <4F4D96F4.3080707@dreamhost.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail.hq.newdream.net ([66.33.206.127]:44141 "EHLO mail.hq.newdream.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030692Ab2B2DMM (ORCPT ); Tue, 28 Feb 2012 22:12:12 -0500 Received: from mail.hq.newdream.net (localhost [127.0.0.1]) by mail.hq.newdream.net (Postfix) with ESMTP id 628E024318 for ; Tue, 28 Feb 2012 19:12:12 -0800 (PST) Received: from [192.168.107.136] (aon.hq.newdream.net [64.111.111.107]) by mail.hq.newdream.net (Postfix) with ESMTPSA id 572A424314 for ; Tue, 28 Feb 2012 19:12:12 -0800 (PST) In-Reply-To: <4F4D96F4.3080707@dreamhost.com> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: ceph-devel@vger.kernel.org A spinlock is used to protect a value used for selecting an array index for a string used for formatting a socket address for human consumption. The index is reset to 0 if it ever reaches the maximum index value. Instead, use an ever-increasing atomic variable as a sequence number, and compute the array index by masking off all but the sequence number's lowest bits. Make the number of entries in the array a power of two to allow the use of such a mask (to avoid jumps in the index value when the sequence number wraps). The length of these strings is somewhat arbitrarily set at 60 bytes. The worst-case length of a string produced is 54 bytes, for an IPv6 address that can't be shortened, e.g.: [1234:5678:9abc:def0:1111:2222:123.234.210.100]:32767 Change it so we arbitrarily use 64 bytes instead; if nothing else it will make the array of these line up better in hex dumps. Rename a few things to reinforce the distinction between the number of strings in the array and the length of individual strings. Signed-off-by: Alex Elder --- net/ceph/messenger.c | 21 ++++++++++----------- 1 files changed, 10 insertions(+), 11 deletions(-) diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c index c9a413a..8edfd1a 100644 --- a/net/ceph/messenger.c +++ b/net/ceph/messenger.c @@ -44,13 +44,16 @@ static void con_work(struct work_struct *); static void ceph_fault(struct ceph_connection *con); /* - * nicely render a sockaddr as a string. + * Nicely render a sockaddr as a string. An array of formatted + * strings is used, to approximate reentrancy. */ -#define MAX_ADDR_STR 20 -#define MAX_ADDR_STR_LEN 60 -static char addr_str[MAX_ADDR_STR][MAX_ADDR_STR_LEN]; -static DEFINE_SPINLOCK(addr_str_lock); -static int last_addr_str; +#define ADDR_STR_COUNT_LOG 5 /* log2(# address strings in array) */ +#define ADDR_STR_COUNT (1 << ADDR_STR_COUNT_LOG) +#define ADDR_STR_COUNT_MASK (ADDR_STR_COUNT - 1) +#define MAX_ADDR_STR_LEN 64 /* 54 is enough */ + +static char addr_str[ADDR_STR_COUNT][MAX_ADDR_STR_LEN]; +static atomic_t addr_str_seq = ATOMIC_INIT(0); static struct page *zero_page; /* used in certain error cases */ static void *zero_page_address; /* kernel virtual addr of zero_page */ @@ -62,11 +65,7 @@ const char *ceph_pr_addr(const struct sockaddr_storage *ss) struct sockaddr_in *in4 = (void *)ss; struct sockaddr_in6 *in6 = (void *)ss; - spin_lock(&addr_str_lock); - i = last_addr_str++; - if (last_addr_str == MAX_ADDR_STR) - last_addr_str = 0; - spin_unlock(&addr_str_lock); + i = atomic_inc_return(&addr_str_seq) & ADDR_STR_COUNT_MASK; s = addr_str[i]; switch (ss->ss_family) { -- 1.7.5.4