[RFC][PATCH] cifs: convert cifs_tcp_ses_lock from a rwlock to a spinlock

[Suresh Jayaraman <sjayaraman-l3A5Bk7waGM@public.gmane.org>]

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-l3A5Bk7waGM@public.gmane.org>
---
 fs/cifs/cifs_debug.c |   12 ++++----
 fs/cifs/cifsfs.c     |    8 +++---
 fs/cifs/cifsglob.h   |    2 +-
 fs/cifs/cifssmb.c    |    6 ++--
 fs/cifs/connect.c    |   70 +++++++++++++++++++++++++-------------------------
 fs/cifs/misc.c       |   14 +++++-----
 fs/cifs/sess.c       |    4 +-
 7 files changed, 58 insertions(+), 58 deletions(-)

diff --git a/fs/cifs/cifs_debug.c b/fs/cifs/cifs_debug.c
index eb1ba49..103ab8b 100644
--- a/fs/cifs/cifs_debug.c
+++ b/fs/cifs/cifs_debug.c
@@ -148,7 +148,7 @@ static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 	seq_printf(m, "Servers:");
 
 	i = 0;
-	read_lock(&cifs_tcp_ses_lock);
+	spin_lock(&cifs_tcp_ses_lock);
 	list_for_each(tmp1, &cifs_tcp_ses_list) {
 		server = list_entry(tmp1, struct TCP_Server_Info,
 				    tcp_ses_list);
@@ -230,7 +230,7 @@ static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 			spin_unlock(&GlobalMid_Lock);
 		}
 	}
-	read_unlock(&cifs_tcp_ses_lock);
+	spin_unlock(&cifs_tcp_ses_lock);
 	seq_putc(m, '\n');
 
 	/* BB add code to dump additional info such as TCP session info now */
@@ -270,7 +270,7 @@ static ssize_t cifs_stats_proc_write(struct file *file,
 		atomic_set(&totBufAllocCount, 0);
 		atomic_set(&totSmBufAllocCount, 0);
 #endif /* CONFIG_CIFS_STATS2 */
-		read_lock(&cifs_tcp_ses_lock);
+		spin_lock(&cifs_tcp_ses_lock);
 		list_for_each(tmp1, &cifs_tcp_ses_list) {
 			server = list_entry(tmp1, struct TCP_Server_Info,
 					    tcp_ses_list);
@@ -303,7 +303,7 @@ static ssize_t cifs_stats_proc_write(struct file *file,
 				}
 			}
 		}
-		read_unlock(&cifs_tcp_ses_lock);
+		spin_unlock(&cifs_tcp_ses_lock);
 	}
 
 	return count;
@@ -343,7 +343,7 @@ static int cifs_stats_proc_show(struct seq_file *m, void *v)
 		GlobalCurrentXid, GlobalMaxActiveXid);
 
 	i = 0;
-	read_lock(&cifs_tcp_ses_lock);
+	spin_lock(&cifs_tcp_ses_lock);
 	list_for_each(tmp1, &cifs_tcp_ses_list) {
 		server = list_entry(tmp1, struct TCP_Server_Info,
 				    tcp_ses_list);
@@ -397,7 +397,7 @@ static int cifs_stats_proc_show(struct seq_file *m, void *v)
 			}
 		}
 	}
-	read_unlock(&cifs_tcp_ses_lock);
+	spin_unlock(&cifs_tcp_ses_lock);
 
 	seq_putc(m, '\n');
 	return 0;
diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index f1d9c71..cb77915 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -482,16 +482,16 @@ static void cifs_umount_begin(struct super_block *sb)
 
 	tcon = cifs_sb_master_tcon(cifs_sb);
 
-	read_lock(&cifs_tcp_ses_lock);
+	spin_lock(&cifs_tcp_ses_lock);
 	if ((tcon->tc_count > 1) || (tcon->tidStatus == CifsExiting)) {
 		/* we have other mounts to same share or we have
 		   already tried to force umount this and woken up
 		   all waiting network requests, nothing to do */
-		read_unlock(&cifs_tcp_ses_lock);
+		spin_unlock(&cifs_tcp_ses_lock);
 		return;
 	} else if (tcon->tc_count == 1)
 		tcon->tidStatus = CifsExiting;
-	read_unlock(&cifs_tcp_ses_lock);
+	spin_unlock(&cifs_tcp_ses_lock);
 
 	/* cancel_brl_requests(tcon); */ /* BB mark all brl mids as exiting */
 	/* cancel_notify_requests(tcon); */
@@ -940,7 +940,7 @@ init_cifs(void)
 	GlobalTotalActiveXid = 0;
 	GlobalMaxActiveXid = 0;
 	memset(Local_System_Name, 0, 15);
-	rwlock_init(&cifs_tcp_ses_lock);
+	spin_lock_init(&cifs_tcp_ses_lock);
 	spin_lock_init(&cifs_file_list_lock);
 	spin_lock_init(&GlobalMid_Lock);
 
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 18ee0ad..28337cb 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -703,7 +703,7 @@ GLOBAL_EXTERN struct list_head		cifs_tcp_ses_list;
  * the reference counters for the server, smb session, and tcon. Finally,
  * changes to the tcon->tidStatus should be done while holding this lock.
  */
-GLOBAL_EXTERN rwlock_t		cifs_tcp_ses_lock;
+GLOBAL_EXTERN spinlock_t		cifs_tcp_ses_lock;
 
 /*
  * This lock protects the cifs_file->llist and cifs_file->flist
diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index bfb59a6..e98f1f3 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -593,9 +593,9 @@ CIFSSMBNegotiate(unsigned int xid, struct cifsSesInfo *ses)
 			rc = -EIO;
 			goto neg_err_exit;
 		}
-		read_lock(&cifs_tcp_ses_lock);
+		spin_lock(&cifs_tcp_ses_lock);
 		if (server->srv_count > 1) {
-			read_unlock(&cifs_tcp_ses_lock);
+			spin_unlock(&cifs_tcp_ses_lock);
 			if (memcmp(server->server_GUID,
 				   pSMBr->u.extended_response.
 				   GUID, 16) != 0) {
@@ -605,7 +605,7 @@ CIFSSMBNegotiate(unsigned int xid, struct cifsSesInfo *ses)
 					16);
 			}
 		} else {
-			read_unlock(&cifs_tcp_ses_lock);
+			spin_unlock(&cifs_tcp_ses_lock);
 			memcpy(server->server_GUID,
 			       pSMBr->u.extended_response.GUID, 16);
 		}
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 @@ cifs_reconnect(struct TCP_Server_Info *server)
 
 	/* 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 @@ cifs_reconnect(struct TCP_Server_Info *server)
 			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 @@ multi_t2_fnd:
 	} /* 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 @@ multi_t2_fnd:
 	 * 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 @@ multi_t2_fnd:
 			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 @@ multi_t2_fnd:
 			}
 		}
 		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 @@ multi_t2_fnd:
 	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 @@ cifs_find_tcp_session(struct sockaddr *addr, struct smb_vol *vol)
 {
 	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 @@ cifs_find_tcp_session(struct sockaddr *addr, struct smb_vol *vol)
 			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 @@ cifs_put_tcp_session(struct TCP_Server_Info *server)
 {
 	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 @@ cifs_get_tcp_session(struct smb_vol *volume_info)
 	}
 
 	/* 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 @@ cifs_find_smb_ses(struct TCP_Server_Info *server, struct smb_vol *vol)
 {
 	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 @@ cifs_find_smb_ses(struct TCP_Server_Info *server, struct smb_vol *vol)
 				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 @@ cifs_put_smb_ses(struct cifsSesInfo *ses)
 	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 @@ cifs_get_smb_ses(struct TCP_Server_Info *server, struct smb_vol *volume_info)
 		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 @@ cifs_find_tcon(struct cifsSesInfo *ses, const char *unc)
 	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 @@ cifs_find_tcon(struct cifsSesInfo *ses, const char *unc)
 			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 @@ cifs_put_tcon(struct cifsTconInfo *tcon)
 	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 @@ cifs_get_tcon(struct cifsSesInfo *ses, struct smb_vol *volume_info)
 	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 @@ cifs_construct_tcon(struct cifs_sb_info *cifs_sb, uid_t fsuid)
 	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)) {
diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index de6073c..a7b492c 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -347,7 +347,7 @@ header_assemble(struct smb_hdr *buffer, char smb_command /* command */ ,
 				if (current_fsuid() != treeCon->ses->linux_uid) {
 					cFYI(1, "Multiuser mode and UID "
 						 "did not match tcon uid");
-					read_lock(&cifs_tcp_ses_lock);
+					spin_lock(&cifs_tcp_ses_lock);
 					list_for_each(temp_item, &treeCon->ses->server->smb_ses_list) {
 						ses = list_entry(temp_item, struct cifsSesInfo, smb_ses_list);
 						if (ses->linux_uid == current_fsuid()) {
@@ -361,7 +361,7 @@ header_assemble(struct smb_hdr *buffer, char smb_command /* command */ ,
 							}
 						}
 					}
-					read_unlock(&cifs_tcp_ses_lock);
+					spin_unlock(&cifs_tcp_ses_lock);
 				}
 			}
 		}
@@ -551,7 +551,7 @@ is_valid_oplock_break(struct smb_hdr *buf, struct TCP_Server_Info *srv)
 		return false;
 
 	/* look up tcon based on tid & uid */
-	read_lock(&cifs_tcp_ses_lock);
+	spin_lock(&cifs_tcp_ses_lock);
 	list_for_each(tmp, &srv->smb_ses_list) {
 		ses = list_entry(tmp, struct cifsSesInfo, smb_ses_list);
 		list_for_each(tmp1, &ses->tcon_list) {
@@ -573,7 +573,7 @@ is_valid_oplock_break(struct smb_hdr *buf, struct TCP_Server_Info *srv)
 				 */
 				if (netfile->closePend) {
 					spin_unlock(&cifs_file_list_lock);
-					read_unlock(&cifs_tcp_ses_lock);
+					spin_unlock(&cifs_tcp_ses_lock);
 					return true;
 				}
 
@@ -595,16 +595,16 @@ is_valid_oplock_break(struct smb_hdr *buf, struct TCP_Server_Info *srv)
 				netfile->oplock_break_cancelled = false;
 
 				spin_unlock(&cifs_file_list_lock);
-				read_unlock(&cifs_tcp_ses_lock);
+				spin_unlock(&cifs_tcp_ses_lock);
 				return true;
 			}
 			spin_unlock(&cifs_file_list_lock);
-			read_unlock(&cifs_tcp_ses_lock);
+			spin_unlock(&cifs_tcp_ses_lock);
 			cFYI(1, "No matching file for oplock break");
 			return true;
 		}
 	}
-	read_unlock(&cifs_tcp_ses_lock);
+	spin_unlock(&cifs_tcp_ses_lock);
 	cFYI(1, "Can not process oplock break for non-existent connection");
 	return true;
 }
diff --git a/fs/cifs/sess.c b/fs/cifs/sess.c
index 2111bed..933ed26 100644
--- a/fs/cifs/sess.c
+++ b/fs/cifs/sess.c
@@ -80,7 +80,7 @@ static __le16 get_next_vcnum(struct cifsSesInfo *ses)
 	if (max_vcs < 2)
 		max_vcs = 0xFFFF;
 
-	write_lock(&cifs_tcp_ses_lock);
+	spin_lock(&cifs_tcp_ses_lock);
 	if ((ses->need_reconnect) && is_first_ses_reconnect(ses))
 			goto get_vc_num_exit;  /* vcnum will be zero */
 	for (i = ses->server->srv_count - 1; i < max_vcs; i++) {
@@ -112,7 +112,7 @@ static __le16 get_next_vcnum(struct cifsSesInfo *ses)
 		vcnum = i;
 	ses->vcnum = vcnum;
 get_vc_num_exit:
-	write_unlock(&cifs_tcp_ses_lock);
+	spin_unlock(&cifs_tcp_ses_lock);
 
 	return cpu_to_le16(vcnum);
 }