[PATCH v5] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()
From: Zheng Yejian <hidden>
Date: 2023-07-12 06:05:04
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 v4 [6] => v5:
- Extract page free logic in ftrace_allocate_pages() as ftrace_free_pages(),
then call it to free unused pages in ftrace_process_locs().
Changes v3 [3] => v4:
- Keep the upside-down-xmas-tree format as Steve suggested [5].
Changes v2 [2] => v3:
- Check NULL for 'pg->next' before assigning it to variable 'pg_unuse'.
Changes v1 [1] => v2:
- As Steve suggested [4], 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.
- Update commit messages about the new solution.
[1] https://lore.kernel.org/all/20230710212958.274126-1-zhengyejian1@huawei.com/ (local)
[2] https://lore.kernel.org/all/20230711201630.1837109-1-zhengyejian1@huawei.com/ (local)
[3] https://lore.kernel.org/all/20230711112752.2595316-1-zhengyejian1@huawei.com/ (local)
[4] https://lore.kernel.org/all/20230710104625.421c851a@gandalf.local.home/ (local)
[5] https://lore.kernel.org/all/20230711095802.71406422@gandalf.local.home/ (local)
[6] https://lore.kernel.org/all/20230712013103.3021978-1-zhengyejian1@huawei.com/ (local)
kernel/trace/ftrace.c | 45 +++++++++++++++++++++++++++++--------------
1 file changed, 31 insertions(+), 14 deletions(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3740aca79fe7..05c0024815bf 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c@@ -3305,6 +3305,22 @@ static int ftrace_allocate_records(struct ftrace_page *pg, int count) return cnt; } +static void ftrace_free_pages(struct ftrace_page *pages) +{ + struct ftrace_page *pg = pages; + + while (pg) { + if (pg->records) { + free_pages((unsigned long)pg->records, pg->order); + ftrace_number_of_pages -= 1 << pg->order; + } + pages = pg->next; + kfree(pg); + pg = pages; + ftrace_number_of_groups--; + } +} + static struct ftrace_page * ftrace_allocate_pages(unsigned long num_to_init) {
@@ -3343,17 +3359,7 @@ ftrace_allocate_pages(unsigned long num_to_init) return start_pg; free_pages: - pg = start_pg; - while (pg) { - if (pg->records) { - free_pages((unsigned long)pg->records, pg->order); - ftrace_number_of_pages -= 1 << pg->order; - } - start_pg = pg->next; - kfree(pg); - pg = start_pg; - ftrace_number_of_groups--; - } + ftrace_free_pages(start_pg); pr_info("ftrace: FAILED to allocate memory for functions\n"); return NULL; }
@@ -6471,9 +6477,11 @@ static int ftrace_process_locs(struct module *mod, unsigned long *start, unsigned long *end) { + struct ftrace_page *pg_unuse = NULL; struct ftrace_page *start_pg; struct ftrace_page *pg; struct dyn_ftrace *rec; + unsigned long skipped = 0; unsigned long count; unsigned long *p; unsigned long addr;
@@ -6536,8 +6544,10 @@ 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 +6561,10 @@ 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 +6586,11 @@ 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); + ftrace_free_pages(pg_unuse); + } return ret; }
--
2.25.1