[Cluster-devel] [PATCH] dlm: remove lock_sock to avoid scheduling while atomic

[Alexander Aring <aahringo@redhat.com>]

From: Bob Peterson <rpeterso@redhat.com>

Before this patch, functions save_callbacks and restore_callbacks
called function lock_sock and release_sock to prevent other processes
from messing with the struct sock while the callbacks were saved and
restored. However, function add_sock calls write_lock_bh prior to
calling it save_callbacks, which disables preempts. So the call to
lock_sock would try to schedule when we can't schedule.

Cc: stable at vger.kernel.org # 4.9.x
Fixes: b81171cb6869 ("DLM: Save and restore socket callbacks properly")
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>
Signed-off-by: Alexander Aring <aahringo@redhat.com>
---
 fs/dlm/lowcomms.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
index 0d8aaf9c61be..9a9fc5ce1166 100644
--- a/fs/dlm/lowcomms.c
+++ b/fs/dlm/lowcomms.c
@@ -519,24 +519,20 @@ static void lowcomms_error_report(struct sock *sk)
 /* Note: sk_callback_lock must be locked before calling this function. */
 static void save_callbacks(struct connection *con, struct sock *sk)
 {
-	lock_sock(sk);
 	con->orig_data_ready = sk->sk_data_ready;
 	con->orig_state_change = sk->sk_state_change;
 	con->orig_write_space = sk->sk_write_space;
 	con->orig_error_report = sk->sk_error_report;
-	release_sock(sk);
 }
 
 static void restore_callbacks(struct connection *con, struct sock *sk)
 {
 	write_lock_bh(&sk->sk_callback_lock);
-	lock_sock(sk);
 	sk->sk_user_data = NULL;
 	sk->sk_data_ready = con->orig_data_ready;
 	sk->sk_state_change = con->orig_state_change;
 	sk->sk_write_space = con->orig_write_space;
 	sk->sk_error_report = con->orig_error_report;
-	release_sock(sk);
 	write_unlock_bh(&sk->sk_callback_lock);
 }
 
-- 
2.27.0