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ceph: kill addr_str_lock spinlock; use atomic instead 

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 <elder@newdream.net>
Signed-off-by: Sage Weil <sage@newdream.net>
This commit is contained in:
Alex Elder 2012-01-23 15:49:27 -06:00
parent a5bc3129a2
commit f64a93172b
1 changed files with 10 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
net/ceph/messenger.c
View File

@ -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) {