cifs: make sure that channel scaling is done only once

Following a successful cifs_tree_connect, we have the code
to scale up/down the number of channels in the session.
However, it is not protected by a lock today.

As a result, this code can be executed by several processes
that select the same channel. The core functions handle this
well, as they pick chan_lock. However, we've seen cases where
smb2_reconnect throws some warnings.

To fix that, this change introduces a flags bitmap inside the
cifs_ses structure. A new flag type is used to ensure that
only one process enters this section at any time.

Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index 16befff4cbb47c9ac104b052401a490398d0fac9..9093c507042fa12ed867bc5297aa5ca8abf50458 100644 (file)
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -1032,6 +1032,8 @@ struct cifs_chan {
        __u8 signkey[SMB3_SIGN_KEY_SIZE];
 };
 
+#define CIFS_SES_FLAG_SCALE_CHANNELS (0x1)
+
 /*
  * Session structure.  One of these for each uid session with a particular host
  */
@@ -1064,6 +1066,7 @@ struct cifs_ses {
        enum securityEnum sectype; /* what security flavor was specified? */
        bool sign;              /* is signing required? */
        bool domainAuto:1;
+       unsigned int flags;
        __u16 session_flags;
        __u8 smb3signingkey[SMB3_SIGN_KEY_SIZE];
        __u8 smb3encryptionkey[SMB3_ENC_DEC_KEY_SIZE];

diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c
index 86f6f35b7f32e8498e2628350abf43daa0d97f96..6db54c6ef5719e1cf9cf8a86846f0589d816d037 100644 (file)
--- a/fs/smb/client/smb2pdu.c
+++ b/fs/smb/client/smb2pdu.c
@@ -399,6 +399,15 @@ skip_sess_setup:
                goto out;
        }
 
+       spin_lock(&ses->ses_lock);
+       if (ses->flags & CIFS_SES_FLAG_SCALE_CHANNELS) {
+               spin_unlock(&ses->ses_lock);
+               mutex_unlock(&ses->session_mutex);
+               goto skip_add_channels;
+       }
+       ses->flags |= CIFS_SES_FLAG_SCALE_CHANNELS;
+       spin_unlock(&ses->ses_lock);
+
        if (!rc &&
            (server->capabilities & SMB2_GLOBAL_CAP_MULTI_CHANNEL)) {
                mutex_unlock(&ses->session_mutex);
@@ -428,17 +437,22 @@ skip_sess_setup:
                if (ses->chan_max > ses->chan_count &&
                    ses->iface_count &&
                    !SERVER_IS_CHAN(server)) {
-                       if (ses->chan_count == 1)
+                       if (ses->chan_count == 1) {
                                cifs_server_dbg(VFS, "supports multichannel now\n");
+                               queue_delayed_work(cifsiod_wq, &tcon->query_interfaces,
+                                                (SMB_INTERFACE_POLL_INTERVAL * HZ));
+                       }
 
                        cifs_try_adding_channels(ses);
-                       queue_delayed_work(cifsiod_wq, &tcon->query_interfaces,
-                                          (SMB_INTERFACE_POLL_INTERVAL * HZ));
                }
        } else {
                mutex_unlock(&ses->session_mutex);
        }
+
 skip_add_channels:
+       spin_lock(&ses->ses_lock);
+       ses->flags &= ~CIFS_SES_FLAG_SCALE_CHANNELS;
+       spin_unlock(&ses->ses_lock);
 
        if (smb2_command != SMB2_INTERNAL_CMD)
                mod_delayed_work(cifsiod_wq, &server->reconnect, 0);