Hello Shyam Prasad N,
The patch e695a9ad0305: "cifs: missed ref-counting smb session in
find" from May 23, 2021 (linux-next), leads to the following Smatch
static checker warning:
fs/smb/client/connect.c:1636 cifs_put_tcp_session()
warn: sleeping in atomic context
What happened here is that we recently shuffled some code around so
now Smatch is aware that cancel_delayed_work_sync() is a might sleep
function.
fs/smb/client/smb2transport.c
204 smb2_find_smb_tcon(struct TCP_Server_Info *server, __u64 ses_id, __u32 tid)
205 {
206 struct cifs_ses *ses;
207 struct cifs_tcon *tcon;
208
209 spin_lock(&cifs_tcp_ses_lock);
210 ses = smb2_find_smb_ses_unlocked(server, ses_id);
211 if (!ses) {
212 spin_unlock(&cifs_tcp_ses_lock);
213 return NULL;
214 }
215 tcon = smb2_find_smb_sess_tcon_unlocked(ses, tid);
216 if (!tcon) {
217 cifs_put_smb_ses(ses);
218 spin_unlock(&cifs_tcp_ses_lock);
Smatch thinks calling cifs_put_smb_ses() might be a problem. This is
a cross function thing involving reference counting and I haven't worked
through where we're holding references so it might be a false positive...
But I see below we drop the lock before calling cifs_put_smb_ses() so
maybe it's okay here too?
219 return NULL;
220 }
221 spin_unlock(&cifs_tcp_ses_lock);
222 /* tcon already has a ref to ses, so we don't need ses anymore */
223 cifs_put_smb_ses(ses);
224
225 return tcon;
226 }
The call tree Smatch warns about is:
smb2_find_smb_tcon() <- disables preempt
-> cifs_put_smb_ses()
-> __cifs_put_smb_ses()
-> cifs_put_tcp_session()
fs/smb/client/connect.c
1617 void
1618 cifs_put_tcp_session(struct TCP_Server_Info *server, int from_reconnect)
1619 {
1620 struct task_struct *task;
1621
1622 spin_lock(&cifs_tcp_ses_lock);
1623 if (--server->srv_count > 0) {
1624 spin_unlock(&cifs_tcp_ses_lock);
1625 return;
1626 }
1627
1628 /* srv_count can never go negative */
1629 WARN_ON(server->srv_count < 0);
1630
1631 put_net(cifs_net_ns(server));
1632
1633 list_del_init(&server->tcp_ses_list);
1634 spin_unlock(&cifs_tcp_ses_lock);
1635
--> 1636 cancel_delayed_work_sync(&server->echo);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Sleeps.
1637
1638 if (from_reconnect)
1639 /*
regards,
dan carpenter
