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Subject[PATCH] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()
Date
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@huawei.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
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