[PATCH v2] ftrace: Fix softlockup in ftrace_module_enable

[Vladimir Riabchun <ferr.lambarginio@gmail.com>]

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 d0b24b4e91fc ("ftrace: Prevent RCU stall on PREEMPT_VOLUNTARY
kernels") and commit 42ea22e754ba ("ftrace: Add cond_resched() to
ftrace_graph_set_hash()").

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

Signed-off-by: Vladimir Riabchun <ferr.lambarginio@gmail.com>
---
Changes since v1: https://lore.kernel.org/all/aMLPm__QGrQCwz1t@vova-pc/
 - Move cond_resched below within_module check
 - Add some details in commit description

kernel/trace/ftrace.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index a69067367c29..42bd2ba68a82 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7535,6 +7535,8 @@ 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 */
-- 
2.43.0