linux-kernel - [PATCH] ftrace: Fix possible warning on checking all pages used in ftrace_process

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Date:   Tue, 11 Jul 2023 05:29:58 +0800
From:   Zheng Yejian <zhengyejian1@...wei.com>
To:     <rostedt@...dmis.org>, <mhiramat@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-trace-kernel@...r.kernel.org>, <zhengyejian1@...wei.com>
Subject: [PATCH] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()

As comments in ftrace_process_locs(), there may be NULL pointers in
mcount_loc section:
 > Some architecture linkers will pad between
 > the different mcount_loc sections of different
 > object files to satisfy alignments.
 > Skip any NULL pointers.

After 20e5227e9f55 ("ftrace: allow NULL pointers in mcount_loc"),
NULL pointers will be accounted when allocating ftrace pages but
skipped before adding into ftrace pages, this may result in some
pages not being used. Then after 706c81f87f84 ("ftrace: Remove extra
helper functions"), warning may occur at:
  WARN_ON(pg->next);

So we may need to skip NULL pointers before allocating ftrace pages.

Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions")
Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
---
 kernel/trace/ftrace.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3740aca79fe7..5b474165df31 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6485,6 +6485,16 @@ static int ftrace_process_locs(struct module *mod,
 	if (!count)
 		return 0;
 
+	p = start;
+	while (p < end) {
+		/*
+		 * Refer to conments below, there may be NULL pointers,
+		 * skip them before allocating pages
+		 */
+		addr = ftrace_call_adjust(*p++);
+		if (!addr)
+			count--;
+	}
 	/*
 	 * Sorting mcount in vmlinux at build time depend on
 	 * CONFIG_BUILDTIME_MCOUNT_SORT, while mcount loc in
-- 
2.25.1