From 5eef12c4e3230f2025dc46ad8c4a3bc19978e5d7 Mon Sep 17 00:00:00 2001 From: Shyam Prasad N Date: Tue, 14 Nov 2023 04:58:23 +0000 Subject: [PATCH] cifs: fix lock ordering while disabling multichannel The code to handle the case of server disabling multichannel was picking iface_lock with chan_lock held. This goes against the lock ordering rules, as iface_lock is a higher order lock (even if it isn't so obvious). This change fixes the lock ordering by doing the following in that order for each secondary channel: 1. store iface and server pointers in local variable 2. remove references to iface and server in channels 3. unlock chan_lock 4. lock iface_lock 5. dec ref count for iface 6. unlock iface_lock 7. dec ref count for server 8. lock chan_lock again Since this function can only be called in smb2_reconnect, and that cannot be called by two parallel processes, we should not have races due to dropping chan_lock between steps 3 and 8. Fixes: ee1d21794e55 ("cifs: handle when server stops supporting multichannel") Reported-by: Paulo Alcantara Signed-off-by: Shyam Prasad N Signed-off-by: Steve French --- fs/smb/client/sess.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-) diff --git a/fs/smb/client/sess.c b/fs/smb/client/sess.c index 0bb2ac929061..8b2d7c1ca428 100644 --- a/fs/smb/client/sess.c +++ b/fs/smb/client/sess.c @@ -322,28 +322,32 @@ cifs_disable_secondary_channels(struct cifs_ses *ses) iface = ses->chans[i].iface; server = ses->chans[i].server; + /* + * remove these references first, since we need to unlock + * the chan_lock here, since iface_lock is a higher lock + */ + ses->chans[i].iface = NULL; + ses->chans[i].server = NULL; + spin_unlock(&ses->chan_lock); + if (iface) { spin_lock(&ses->iface_lock); kref_put(&iface->refcount, release_iface); - ses->chans[i].iface = NULL; iface->num_channels--; if (iface->weight_fulfilled) iface->weight_fulfilled--; spin_unlock(&ses->iface_lock); } - spin_unlock(&ses->chan_lock); - if (server && !server->terminate) { - server->terminate = true; - cifs_signal_cifsd_for_reconnect(server, false); - } - spin_lock(&ses->chan_lock); - if (server) { - ses->chans[i].server = NULL; + if (!server->terminate) { + server->terminate = true; + cifs_signal_cifsd_for_reconnect(server, false); + } cifs_put_tcp_session(server, false); } + spin_lock(&ses->chan_lock); } done: