ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()

commit 26efd79c4624294e553aeaa3439c646729bad084 upstream.

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.

Link: https://lore.kernel.org/linux-trace-kernel/20230712060452.3175675-1-zhengyejian1@huawei.com
Cc: stable@vger.kernel.org
Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 57db50c..552956c 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3213,6 +3213,22 @@ 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)
 {
@@ -3251,17 +3267,7 @@ 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;
 }
@@ -6666,9 +6672,11 @@ 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;
@@ -6731,8 +6739,10 @@ 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) {
@@ -6746,8 +6756,10 @@ 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;
@@ -6769,6 +6781,11 @@ 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;
 }