cifs: convert cifs_tcp_ses_lock from a rwlock to a spinlock
cifs_tcp_ses_lock is a rwlock with protects the cifs_tcp_ses_list,
server->smb_ses_list and the ses->tcon_list. It also protects a few
ref counters in server, ses and tcon. In most cases the critical section
doesn't seem to be large, in a few cases where it is slightly large, there
seem to be really no benefit from concurrent access. I briefly considered RCU
mechanism but it appears to me that there is no real need.
Replace it with a spinlock and get rid of the last rwlock in the cifs code.
Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 019f003..7e73176 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -150,7 +150,7 @@
/* before reconnecting the tcp session, mark the smb session (uid)
and the tid bad so they are not used until reconnected */
- read_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
list_for_each(tmp, &server->smb_ses_list) {
ses = list_entry(tmp, struct cifsSesInfo, smb_ses_list);
ses->need_reconnect = true;
@@ -160,7 +160,7 @@
tcon->need_reconnect = true;
}
}
- read_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
/* do not want to be sending data on a socket we are freeing */
mutex_lock(&server->srv_mutex);
if (server->ssocket) {
@@ -637,9 +637,9 @@
} /* end while !EXITING */
/* take it off the list, if it's not already */
- write_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
list_del_init(&server->tcp_ses_list);
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
spin_lock(&GlobalMid_Lock);
server->tcpStatus = CifsExiting;
@@ -677,7 +677,7 @@
* BB: we shouldn't have to do any of this. It shouldn't be
* possible to exit from the thread with active SMB sessions
*/
- read_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
if (list_empty(&server->pending_mid_q)) {
/* loop through server session structures attached to this and
mark them dead */
@@ -687,7 +687,7 @@
ses->status = CifsExiting;
ses->server = NULL;
}
- read_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
} else {
/* although we can not zero the server struct pointer yet,
since there are active requests which may depnd on them,
@@ -710,7 +710,7 @@
}
}
spin_unlock(&GlobalMid_Lock);
- read_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
/* 1/8th of sec is more than enough time for them to exit */
msleep(125);
}
@@ -733,12 +733,12 @@
if a crazy root user tried to kill cifsd
kernel thread explicitly this might happen) */
/* BB: This shouldn't be necessary, see above */
- read_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
list_for_each(tmp, &server->smb_ses_list) {
ses = list_entry(tmp, struct cifsSesInfo, smb_ses_list);
ses->server = NULL;
}
- read_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
kfree(server->hostname);
task_to_wake = xchg(&server->tsk, NULL);
@@ -1524,7 +1524,7 @@
{
struct TCP_Server_Info *server;
- write_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
list_for_each_entry(server, &cifs_tcp_ses_list, tcp_ses_list) {
if (!match_address(server, addr,
(struct sockaddr *)&vol->srcaddr))
@@ -1534,11 +1534,11 @@
continue;
++server->srv_count;
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
cFYI(1, "Existing tcp session with server found");
return server;
}
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
return NULL;
}
@@ -1547,14 +1547,14 @@
{
struct task_struct *task;
- write_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
if (--server->srv_count > 0) {
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
return;
}
list_del_init(&server->tcp_ses_list);
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
spin_lock(&GlobalMid_Lock);
server->tcpStatus = CifsExiting;
@@ -1679,9 +1679,9 @@
}
/* thread spawned, put it on the list */
- write_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
list_add(&tcp_ses->tcp_ses_list, &cifs_tcp_ses_list);
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
cifs_fscache_get_client_cookie(tcp_ses);
@@ -1703,7 +1703,7 @@
{
struct cifsSesInfo *ses;
- write_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
switch (server->secType) {
case Kerberos:
@@ -1723,10 +1723,10 @@
continue;
}
++ses->ses_count;
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
return ses;
}
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
return NULL;
}
@@ -1737,14 +1737,14 @@
struct TCP_Server_Info *server = ses->server;
cFYI(1, "%s: ses_count=%d\n", __func__, ses->ses_count);
- write_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
if (--ses->ses_count > 0) {
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
return;
}
list_del_init(&ses->smb_ses_list);
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
if (ses->status == CifsGood) {
xid = GetXid();
@@ -1841,9 +1841,9 @@
goto get_ses_fail;
/* success, put it on the list */
- write_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
list_add(&ses->smb_ses_list, &server->smb_ses_list);
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
FreeXid(xid);
return ses;
@@ -1860,7 +1860,7 @@
struct list_head *tmp;
struct cifsTconInfo *tcon;
- write_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
list_for_each(tmp, &ses->tcon_list) {
tcon = list_entry(tmp, struct cifsTconInfo, tcon_list);
if (tcon->tidStatus == CifsExiting)
@@ -1869,10 +1869,10 @@
continue;
++tcon->tc_count;
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
return tcon;
}
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
return NULL;
}
@@ -1883,14 +1883,14 @@
struct cifsSesInfo *ses = tcon->ses;
cFYI(1, "%s: tc_count=%d\n", __func__, tcon->tc_count);
- write_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
if (--tcon->tc_count > 0) {
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
return;
}
list_del_init(&tcon->tcon_list);
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
xid = GetXid();
CIFSSMBTDis(xid, tcon);
@@ -1963,9 +1963,9 @@
tcon->nocase = volume_info->nocase;
tcon->local_lease = volume_info->local_lease;
- write_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
list_add(&tcon->tcon_list, &ses->tcon_list);
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
cifs_fscache_get_super_cookie(tcon);
@@ -3225,9 +3225,9 @@
vol_info->secFlg = CIFSSEC_MUST_KRB5;
/* get a reference for the same TCP session */
- write_lock(&cifs_tcp_ses_lock);
+ spin_lock(&cifs_tcp_ses_lock);
++master_tcon->ses->server->srv_count;
- write_unlock(&cifs_tcp_ses_lock);
+ spin_unlock(&cifs_tcp_ses_lock);
ses = cifs_get_smb_ses(master_tcon->ses->server, vol_info);
if (IS_ERR(ses)) {