ftrace: Fix softlockup in ftrace_module_enable

[ Upstream commit 4099b98 ]

A soft lockup was observed when loading amdgpu module.
If a module has a lot of tracable functions, multiple calls
to kallsyms_lookup can spend too much time in RCU critical
section and with disabled preemption, causing kernel panic.
This is the same issue that was fixed in
commit d0b24b4 ("ftrace: Prevent RCU stall on PREEMPT_VOLUNTARY
kernels") and commit 42ea22e ("ftrace: Add cond_resched() to
ftrace_graph_set_hash()").

Fix it the same way by adding cond_resched() in ftrace_module_enable.

Link: https://lore.kernel.org/aMQD9_lxYmphT-up@vova-pc
Signed-off-by: Vladimir Riabchun <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
(cherry picked from commit e81e6d6d99b16dae11adbeda5c996317942a940c)
Signed-off-by: Wentao Guan <[email protected]>

Author: Frankenween

kernel/trace/ftrace.c

@@ -6873,6 +6873,8 @@ void ftrace_module_enable(struct module *mod)
 		if (!within_module(rec->ip, mod))
 			break;
 
+		cond_resched();
+
 		/* Weak functions should still be ignored */
 		if (!test_for_valid_rec(rec)) {
 			/* Clear all other flags. Should not be enabled anyway */