[PATCH 6.4 542/800] cifs: do all necessary checks for credits within or before locking

Greg Kroah-Hartman
2023-07-16T20:18:11Z

From: Shyam Prasad N <sprasad@microsoft.com>

[ Upstream commit 326a8d04f147e2bf393f6f9cdb74126ee6900607 ]

All the server credits and in-flight info is protected by req_lock.
Once the req_lock is held, and we've determined that we have enough
credits to continue, this lock cannot be dropped till we've made the
changes to credits and in-flight count.

However, we used to drop the lock in order to avoid deadlock with
the recent srv_lock. This could cause the checks already made to be
invalidated.

Fixed it by moving the server status check to before locking req_lock.

Fixes: d7d7a66aacd6 ("cifs: avoid use of global locks for high contention data")
Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/smb/client/smb2ops.c | 19 ++++++++++---------
fs/smb/client/transport.c | 20 ++++++++++----------
2 files changed, 20 insertions(+), 19 deletions(-)

diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index a8bb9d00d33ad..3bac586e8a8eb 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -211,6 +211,16 @@ smb2_wait_mtu_credits(struct TCP_Server_Info *server, unsigned int size,

spin_lock(&server->req_lock);
while (1) {
+ spin_unlock(&server->req_lock);
+
+ spin_lock(&server->srv_lock);
+ if (server->tcpStatus == CifsExiting) {
+ spin_unlock(&server->srv_lock);
+ return -ENOENT;
+ }
+ spin_unlock(&server->srv_lock);
+
+ spin_lock(&server->req_lock);
if (server->credits <= 0) {
spin_unlock(&server->req_lock);
cifs_num_waiters_inc(server);
@@ -221,15 +231,6 @@ smb2_wait_mtu_credits(struct TCP_Server_Info *server, unsigned int size,
return rc;
spin_lock(&server->req_lock);
} else {
- spin_unlock(&server->req_lock);
- spin_lock(&server->srv_lock);
- if (server->tcpStatus == CifsExiting) {
- spin_unlock(&server->srv_lock);
- return -ENOENT;
- }
- spin_unlock(&server->srv_lock);
-
- spin_lock(&server->req_lock);
scredits = server->credits;
/* can deadlock with reopen */
if (scredits <= 8) {
diff --git a/fs/smb/client/transport.c b/fs/smb/client/transport.c
index 0474d0bba0a2e..f280502a2aee8 100644
--- a/fs/smb/client/transport.c
+++ b/fs/smb/client/transport.c
@@ -522,6 +522,16 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits,
}

while (1) {
+ spin_unlock(&server->req_lock);
+
+ spin_lock(&server->srv_lock);
+ if (server->tcpStatus == CifsExiting) {
+ spin_unlock(&server->srv_lock);
+ return -ENOENT;
+ }
+ spin_unlock(&server->srv_lock);
+
+ spin_lock(&server->req_lock);
if (*credits < num_credits) {
scredits = *credits;
spin_unlock(&server->req_lock);
@@ -547,15 +557,6 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits,
return -ERESTARTSYS;
spin_lock(&server->req_lock);
} else {
- spin_unlock(&server->req_lock);
-
- spin_lock(&server->srv_lock);
- if (server->tcpStatus == CifsExiting) {
- spin_unlock(&server->srv_lock);
- return -ENOENT;
- }
- spin_unlock(&server->srv_lock);
-
/*
* For normal commands, reserve the last MAX_COMPOUND
* credits to compound requests.
@@ -569,7 +570,6 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits,
* for servers that are slow to hand out credits on
* new sessions.
*/
- spin_lock(&server->req_lock);
if (!optype && num_credits == 1 &&
server->in_flight > 2 * MAX_COMPOUND &&
*credits <= MAX_COMPOUND) {
--
2.39.2