[PATCH] afs: Fix potential null pointer dereference in afs_put_server

[Zhen Ni]

afs_put_server() accessed server->debug_id before the NULL check, which
could lead to a null pointer dereference. Move the debug_id assignment,
ensuring we never dereference a NULL server pointer.

Fixes: 2757a4dc1849 ("afs: Fix access after dec in put functions")
Cc: stable at vger.kernel.org
Signed-off-by: Zhen Ni <zhen.ni at easystack.cn>
---
 fs/afs/server.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/afs/server.c b/fs/afs/server.c
index a97562f831eb..c4428ebddb1d 100644
--- a/fs/afs/server.c
+++ b/fs/afs/server.c
@@ -331,13 +331,14 @@ struct afs_server *afs_use_server(struct afs_server *server, bool activate,
 void afs_put_server(struct afs_net *net, struct afs_server *server,
 		    enum afs_server_trace reason)
 {
-	unsigned int a, debug_id = server->debug_id;
+	unsigned int a, debug_id;
 	bool zero;
 	int r;
 
 	if (!server)
 		return;
 
+	debug_id = server->debug_id;
 	a = atomic_read(&server->active);
 	zero = __refcount_dec_and_test(&server->ref, &r);
 	trace_afs_server(debug_id, r - 1, a, reason);
-- 
2.20.1