[v3] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()
Commit Message
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 <zhengyejian1@huawei.com>
---
Changes v2 -> v3: https://lore.kernel.org/all/20230711201630.1837109-1-zhengyejian1@huawei.com/
- 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/
- 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(-)
@@ -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;
}