From: Ronnie Sahlberg <lsahlber@redhat.com>
Date: Mon, 11 Mar 2019 12:18:58 +1000
Subject: [PATCH] cifs: simplify how we handle credits in compound_send_recv()
Git-commit: 257b78099be015762b1b19b3e4c58f90a9913fb7
Patch-mainline: v5.1-rc1
References: bsc#1144333
Since we can now wait for multiple requests atomically in
wait_for_free_request() we can now greatly simplify the handling
of the credits in this function.
This fixes a potential deadlock where many concurrent compound requests
could each have reserved 1 or 2 credits each but are all blocked
waiting for the final credits they need to be able to issue the requests
to the server.
Set a default timeout of 60 seconds for compounded requests.
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Acked-by: Aurelien Aptel <aaptel@suse.com>
---
fs/cifs/transport.c | 110 ++++++++++++++++++----------------------------------
1 file changed, 38 insertions(+), 72 deletions(-)
diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index 8731cfa66026..1de8e996e566 100644
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -606,6 +606,31 @@ wait_for_free_request(struct TCP_Server_Info *server, const int flags,
instance);
}
+static int
+wait_for_compound_request(struct TCP_Server_Info *server, int num,
+ const int flags, unsigned int *instance)
+{
+ int *credits;
+
+ credits = server->ops->get_credits_field(server, flags & CIFS_OP_MASK);
+
+ spin_lock(&server->req_lock);
+ if (*credits < num) {
+ /*
+ * Return immediately if not too many requests in flight since
+ * we will likely be stuck on waiting for credits.
+ */
+ if (server->in_flight < num - *credits) {
+ spin_unlock(&server->req_lock);
+ return -ENOTSUPP;
+ }
+ }
+ spin_unlock(&server->req_lock);
+
+ return wait_for_free_credits(server, num, 60000, flags,
+ instance);
+}
+
int
cifs_wait_mtu_credits(struct TCP_Server_Info *server, unsigned int size,
unsigned int *num, struct cifs_credits *credits)
@@ -934,7 +959,6 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses,
{ .value = 0, .instance = 0 }
};
unsigned int instance;
- unsigned int first_instance = 0;
char *buf;
optype = flags & CIFS_OP_MASK;
@@ -950,80 +974,24 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses,
if (ses->server->tcpStatus == CifsExiting)
return -ENOENT;
- spin_lock(&ses->server->req_lock);
- if (ses->server->credits < num_rqst) {
- /*
- * Return immediately if not too many requests in flight since
- * we will likely be stuck on waiting for credits.
- */
- if (ses->server->in_flight < num_rqst - ses->server->credits) {
- spin_unlock(&ses->server->req_lock);
- return -ENOTSUPP;
- }
- } else {
- /* enough credits to send the whole compounded request */
- ses->server->credits -= num_rqst;
- ses->server->in_flight += num_rqst;
- first_instance = ses->server->reconnect_instance;
- }
- spin_unlock(&ses->server->req_lock);
-
- if (first_instance) {
- cifs_dbg(FYI, "Acquired %d credits at once\n", num_rqst);
- for (i = 0; i < num_rqst; i++) {
- credits[i].value = 1;
- credits[i].instance = first_instance;
- }
- goto setup_rqsts;
- }
-
/*
- * There are not enough credits to send the whole compound request but
- * there are requests in flight that may bring credits from the server.
+ * Wait for all the requests to become available.
* This approach still leaves the possibility to be stuck waiting for
* credits if the server doesn't grant credits to the outstanding
- * requests. This should be fixed by returning immediately and letting
- * a caller fallback to sequential commands instead of compounding.
- * Ensure we obtain 1 credit per request in the compound chain.
+ * requests and if the client is completely idle, not generating any
+ * other requests.
+ * This can be handled by the eventual session reconnect.
*/
- for (i = 0; i < num_rqst; i++) {
- rc = wait_for_free_request(ses->server, flags, &instance);
-
- if (rc == 0) {
- credits[i].value = 1;
- credits[i].instance = instance;
- /*
- * All parts of the compound chain must get credits from
- * the same session, otherwise we may end up using more
- * credits than the server granted. If there were
- * reconnects in between, return -EAGAIN and let callers
- * handle it.
- */
- if (i == 0)
- first_instance = instance;
- else if (first_instance != instance) {
- i++;
- rc = -EAGAIN;
- }
- }
+ rc = wait_for_compound_request(ses->server, num_rqst, flags,
+ &instance);
+ if (rc)
+ return rc;
- if (rc) {
- /*
- * We haven't sent an SMB packet to the server yet but
- * we already obtained credits for i requests in the
- * compound chain - need to return those credits back
- * for future use. Note that we need to call add_credits
- * multiple times to match the way we obtained credits
- * in the first place and to account for in flight
- * requests correctly.
- */
- for (j = 0; j < i; j++)
- add_credits(ses->server, &credits[j], optype);
- return rc;
- }
+ for (i = 0; i < num_rqst; i++) {
+ credits[i].value = 1;
+ credits[i].instance = instance;
}
-setup_rqsts:
/*
* Make sure that we sign in the same order that we send on this socket
* and avoid races inside tcp sendmsg code that could cause corruption
@@ -1034,14 +1002,12 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses,
/*
* All the parts of the compound chain belong obtained credits from the
- * same session (see the appropriate checks above). In the same time
- * there might be reconnects after those checks but before we acquired
- * the srv_mutex. We can not use credits obtained from the previous
+ * same session. We can not use credits obtained from the previous
* session to send this request. Check if there were reconnects after
* we obtained credits and return -EAGAIN in such cases to let callers
* handle it.
*/
- if (first_instance != ses->server->reconnect_instance) {
+ if (instance != ses->server->reconnect_instance) {
mutex_unlock(&ses->server->srv_mutex);
for (j = 0; j < num_rqst; j++)
add_credits(ses->server, &credits[j], optype);
--
2.16.4