Re: [PATCH v3 1/2] ftrace: disable preemption between ftrace_test_recursion_trylock/unlock()

On 2021/10/14 下午5:13, Miroslav Benes wrote:

quoted

diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index e8029ae..b8d75fb 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c

@@ -49,14 +49,16 @@ static void notrace klp_ftrace_handler(unsigned long ip,

 	ops = container_of(fops, struct klp_ops, fops);

+	/*
+	 *

This empty line is not useful.

quoted

+	 * The ftrace_test_recursion_trylock() will disable preemption,
+	 * which is required for the variant of synchronize_rcu() that is
+	 * used to allow patching functions where RCU is not watching.
+	 * See klp_synchronize_transition() for more details.
+	 */
 	bit = ftrace_test_recursion_trylock(ip, parent_ip);
 	if (WARN_ON_ONCE(bit < 0))
 		return;
-	/*
-	 * A variant of synchronize_rcu() is used to allow patching functions
-	 * where RCU is not watching, see klp_synchronize_transition().
-	 */
-	preempt_disable_notrace();

 	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
 				      stack_node);

@@ -120,7 +122,6 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 	klp_arch_set_pc(fregs, (unsigned long)func->new_func);

 unlock:
-	preempt_enable_notrace();
 	ftrace_test_recursion_unlock(bit);
 }

Acked-by: Miroslav Benes <mbenes@suse.cz>

for the livepatch part of the patch.

I would also ask you not to submit new versions so often, so that the 
other reviewers have time to actually review the patch set.

Quoting from Documentation/process/submitting-patches.rst:

"Wait for a minimum of one week before resubmitting or pinging reviewers - 
possibly longer during busy times like merge windows."

Thanks for the Ack and suggestion, will take care from now on :-)

Regards,
Michael Wang

Thanks

Miroslav