The pg_remaining calculation in ftrace_process_locs() assumes that
ENTRIES_PER_PAGE multiplied by 2^order equals the actual capacity of the
allocated page group. However, ENTRIES_PER_PAGE is PAGE_SIZE / ENTRY_SIZE
(integer division). When PAGE_SIZE is not a multiple of ENTRY_SIZE (e.g.
4096 / 24 = 170 with remainder 16), high-order allocations (like 256 pages)
have significantly more capacity than 256 * 170. This leads to pg_remaining
being underestimated, which in turn makes skip (derived from skipped -
pg_remaining) larger than expected, causing the WARN(skip != remaining)
to trigger.
Extra allocated pages for ftrace: 2 with 654 skipped
WARNING: CPU: 0 PID: 0 at kernel/trace/ftrace.c:7295
ftrace_process_locs+0x5bf/0x5e0
A similar problem in ftrace_allocate_records() can result in allocating
too many pages. This can trigger the second warning in
ftrace_process_locs().
Extra allocated pages for ftrace
WARNING: CPU: 0 PID: 0 at kernel/trace/ftrace.c:7276
ftrace_process_locs+0x548/0x580
Use the actual capacity of a page group to determine if too many pages
have been allocated to solve the problem. Also use the actual capacity
of a page group to determine the number of pages needed to avoid over-
allocations in ftrace_allocate_records().
Fixes: 4a3efc6baff93 ("ftrace: Update the mcount_loc check of skipped entries")
Cc: Steven Rostedt <[email protected]>
Signed-off-by: Guenter Roeck <[email protected]>
---
kernel/trace/ftrace.c | 25 +++++++++++++++++--------
1 file changed, 17 insertions(+), 8 deletions(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index ef2d5dca6f70..211ec7a04f7e 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3844,7 +3844,7 @@ static int ftrace_allocate_records(struct ftrace_page
*pg, int count)
return -EINVAL;
/* We want to fill as much as possible, with no empty pages */
- pages = DIV_ROUND_UP(count, ENTRIES_PER_PAGE);
+ pages = DIV_ROUND_UP(count * ENTRY_SIZE, PAGE_SIZE);
order = fls(pages) - 1;
again:
@@ -7308,24 +7308,33 @@ static int ftrace_process_locs(struct module *mod,
unsigned long skip;
/* Count the number of entries unused and compare it to
skipped. */
- pg_remaining = (ENTRIES_PER_PAGE << pg->order) - pg->index;
+ pg_remaining = (PAGE_SIZE << pg->order) / ENTRY_SIZE -
pg->index;
if (!WARN(skipped < pg_remaining, "Extra allocated pages for
ftrace")) {
+ unsigned long space = 0;
skip = skipped - pg_remaining;
- for (pg = pg_unuse; pg; pg = pg->next)
+ for (pg = pg_unuse; pg; pg = pg->next) {
remaining += 1 << pg->order;
+ /*
+ * The capacity of a page group is
+ * (PAGE_SIZE << order) / ENTRY_SIZE
+ * Accumulate the total capacity of unused
pages.
+ */
+ space += (PAGE_SIZE << pg->order) / ENTRY_SIZE;
+ }
pages -= remaining;
- skip = DIV_ROUND_UP(skip, ENTRIES_PER_PAGE);
-
/*
- * Check to see if the number of pages remaining would
- * just fit the number of entries skipped.
+ * Check to see if extra pages have been allocated.
+ * Only warn if the number of unused entries is larger
+ * than the number of entries per page to avoid false
+ * positives due to rounding.
*/
- WARN(skip != remaining, "Extra allocated pages for
ftrace: %lu with %lu skipped",
+ WARN(space - skip > ENTRIES_PER_PAGE,
+ "Extra allocated pages for ftrace: %lu with %lu
skipped",
remaining, skipped);
}
/* Need to synchronize with ftrace_location_range() */
--
2.45.2
