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cifs: do all necessary checks for credits within or before locking 

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: d7d7a66aac ("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>
This commit is contained in:
Shyam Prasad N 2023-06-22 18:16:04 +00:00 committed by Steve French
parent 33f736187d
commit 326a8d04f1
2 changed files with 20 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
fs/smb/client/smb2ops.c
View File

@ -215,6 +215,16 @@ 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);
@ -225,15 +235,6 @@ 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) {

20
fs/smb/client/transport.c
View File

@ -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) {