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cifs: fix lock ordering while disabling multichannel

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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: ee1d21794e ("cifs: handle when server stops supporting multichannel")
Reported-by: Paulo Alcantara <pc@manguebit.com>
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 2023-11-14 04:58:23 +00:00 committed by Steve French
parent 29954d5b1e
commit 5eef12c4e3
1 changed files with 13 additions and 9 deletions
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22
fs/smb/client/sess.c
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@ -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: