[PATCH AUTOSEL 6.7 28/44] cifs: make sure that channel scaling is done only once

Sasha Levin
2024-02-07T21:22:54Z

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

[ Upstream commit ee36a3b345c433a846effcdcfba437c2298eeda5 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/smb/client/cifsglob.h | 3 +++
fs/smb/client/smb2pdu.c | 18 +++++++++++++++++-
2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index 5e32c79f03a7..75ca732a1679 100644
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -1004,6 +1004,8 @@ 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
*/
@@ -1036,6 +1038,7 @@ 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 f5006aa97f5b..ab8765113392 100644
--- a/fs/smb/client/smb2pdu.c
+++ b/fs/smb/client/smb2pdu.c
@@ -399,6 +399,15 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
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);
@@ -428,15 +437,22 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
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);
}
} 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);
--
2.43.0