[PATCH v3] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()
From: Zheng Yejian <hidden>
Date: 2023-07-11 11:28:12
Also in:
lkml
Subsystem:
function hooks (ftrace), the rest, tracing · Maintainers:
Steven Rostedt, Masami Hiramatsu, Linus Torvalds
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 commit 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 commit 706c81f87f84 ("ftrace: Remove extra helper
functions"), warning may occur at:
WARN_ON(pg->next);
To fix it, only warn for case that no pointers skipped but pages not used
up, then free those unused pages after releasing ftrace_lock.
Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Zheng Yejian <redacted>
---
Changes v2 -> v3: https://lore.kernel.org/all/20230711201630.1837109-1-zhengyejian1@huawei.com/ (local)
- Check NULL for 'pg->next' before assigning it to variable 'pg_unuse'
Changes v1 -> v2: https://lore.kernel.org/all/20230710104625.421c851a@gandalf.local.home/ (local)
- As suggested by Steve, only warn for case that no pointers skipped
but pages not used up then free those unused pages. But I move the
free process after releasing ftrace_lock.
kernel/trace/ftrace.c | 26 +++++++++++++++++++++++---
1 file changed, 23 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3740aca79fe7..e43e21a3d5fd 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c@@ -6473,7 +6473,9 @@ static int ftrace_process_locs(struct module *mod, { struct ftrace_page *start_pg; struct ftrace_page *pg; + struct ftrace_page *pg_unuse = NULL; struct dyn_ftrace *rec; + unsigned long skipped = 0; unsigned long count; unsigned long *p; unsigned long addr;
@@ -6536,8 +6538,10 @@ static int ftrace_process_locs(struct module *mod, * object files to satisfy alignments. * Skip any NULL pointers. */ - if (!addr) + if (!addr) { + skipped++; continue; + } end_offset = (pg->index+1) * sizeof(pg->records[0]); if (end_offset > PAGE_SIZE << pg->order) {
@@ -6551,8 +6555,10 @@ static int ftrace_process_locs(struct module *mod, rec->ip = addr; } - /* We should have used all pages */ - WARN_ON(pg->next); + if (pg->next) { + pg_unuse = pg->next; + pg->next = NULL; + } /* Assign the last page to ftrace_pages */ ftrace_pages = pg;
@@ -6574,6 +6580,20 @@ static int ftrace_process_locs(struct module *mod, out: mutex_unlock(&ftrace_lock); + /* We should have used all pages unless we skipped some */ + if (pg_unuse) { + WARN_ON(!skipped); + while (pg_unuse) { + pg = pg_unuse; + pg_unuse = pg->next; + if (pg->records) { + free_pages((unsigned long)pg->records, pg->order); + ftrace_number_of_pages -= 1 << pg->order; + } + kfree(pg); + ftrace_number_of_groups--; + } + } return ret; }
--
2.25.1