SUNRPC: Prevent looping due to rpc_signal_task() races

JIRA: https://issues.redhat.com/browse/RHEL-108616

commit 5bbd6e8
Author: Trond Myklebust <trond.myklebust@hammerspace.com>
Date:   Sat Feb 1 15:00:02 2025 -0500

    SUNRPC: Prevent looping due to rpc_signal_task() races

    If rpc_signal_task() is called while a task is in an rpc_call_done()
    callback function, and the latter calls rpc_restart_call(), the task can
    end up looping due to the RPC_TASK_SIGNALLED flag being set without the
    tk_rpc_status being set.
    Removing the redundant mechanism for signalling the task fixes the
    looping behaviour.

    Reported-by: Li Lingfeng <lilingfeng3@huawei.com>
    Fixes: 3949419 ("SUNRPC: Fix races with rpc_killall_tasks()")
    Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
    Reviewed-by: Jeff Layton <jlayton@kernel.org>
    Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>

Author: bcodding-rh

include/linux/sunrpc/sched.h

@@ -158,7 +158,6 @@ enum {
 	RPC_TASK_NEED_XMIT,
 	RPC_TASK_NEED_RECV,
 	RPC_TASK_MSG_PIN_WAIT,
-	RPC_TASK_SIGNALLED,
 };
 
 #define rpc_test_and_set_running(t) \
@@ -171,7 +170,7 @@ enum {
 
 #define RPC_IS_ACTIVATED(t)	test_bit(RPC_TASK_ACTIVE, &(t)->tk_runstate)
 
-#define RPC_SIGNALLED(t)	test_bit(RPC_TASK_SIGNALLED, &(t)->tk_runstate)
+#define RPC_SIGNALLED(t)	(READ_ONCE(task->tk_rpc_status) == -ERESTARTSYS)
 
 /*
  * Task priorities.

include/trace/events/sunrpc.h

@@ -360,8 +360,7 @@ TRACE_EVENT(rpc_request,
 		{ (1UL << RPC_TASK_ACTIVE), "ACTIVE" },			\
 		{ (1UL << RPC_TASK_NEED_XMIT), "NEED_XMIT" },		\
 		{ (1UL << RPC_TASK_NEED_RECV), "NEED_RECV" },		\
-		{ (1UL << RPC_TASK_MSG_PIN_WAIT), "MSG_PIN_WAIT" },	\
-		{ (1UL << RPC_TASK_SIGNALLED), "SIGNALLED" })
+		{ (1UL << RPC_TASK_MSG_PIN_WAIT), "MSG_PIN_WAIT" })
 
 DECLARE_EVENT_CLASS(rpc_task_running,
 

net/sunrpc/sched.c

@@ -864,8 +864,6 @@ void rpc_signal_task(struct rpc_task *task)
 	if (!rpc_task_set_rpc_status(task, -ERESTARTSYS))
 		return;
 	trace_rpc_task_signalled(task, task->tk_action);
-	set_bit(RPC_TASK_SIGNALLED, &task->tk_runstate);
-	smp_mb__after_atomic();
 	queue = READ_ONCE(task->tk_waitqueue);
 	if (queue)
 		rpc_wake_up_queued_task(queue, task);