Messages in this thread Patch in this message | | | From | Zheng Yejian <> | Subject | [PATCH v4] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs() | Date | Wed, 12 Jul 2023 09:31:03 +0800 |
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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 v3 [3] => v4: - Keep the upside-down-xmas-tree format as Steve suggested. Link: https://lore.kernel.org/all/20230711095802.71406422@gandalf.local.home/
Changes v2 [2] => v3: - Check NULL for 'pg->next' before assigning it to variable 'pg_unuse'.
Changes v1 [1] => v2: - As Steve suggested, 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. Link: https://lore.kernel.org/all/20230710104625.421c851a@gandalf.local.home/ - Update commit messages about the new solution.
[1] https://lore.kernel.org/all/20230710212958.274126-1-zhengyejian1@huawei.com/ [2] https://lore.kernel.org/all/20230711201630.1837109-1-zhengyejian1@huawei.com/ [3] https://lore.kernel.org/all/20230711112752.2595316-1-zhengyejian1@huawei.com/
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..6fc238f6ef3e 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -6471,9 +6471,11 @@ 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 +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
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