On 17.02.2022 16:23, Eric Dumazet wrote:
On Thu, Feb 17, 2022 at 6:05 AM Andrzej Hajda <andrzej.hajda@xxxxxxxxx> wrote:
In cases references are taken alternately on multiple exec paths leak
report can grow substantially, sorting and grouping leaks by stack_handle
allows to compact it.
Signed-off-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
Reviewed-by: Chris Wilson <chris.p.wilson@xxxxxxxxx>
---
lib/ref_tracker.c | 35 +++++++++++++++++++++++++++--------
1 file changed, 27 insertions(+), 8 deletions(-)
diff --git a/lib/ref_tracker.c b/lib/ref_tracker.c
index 1b0c6d645d64a..0e9c7d2828ccb 100644
--- a/lib/ref_tracker.c
+++ b/lib/ref_tracker.c
@@ -1,5 +1,6 @@
// SPDX-License-Identifier: GPL-2.0-or-later
#include <linux/export.h>
+#include <linux/list_sort.h>
#include <linux/ref_tracker.h>
#include <linux/slab.h>
#include <linux/stacktrace.h>
@@ -14,23 +15,41 @@ struct ref_tracker {
depot_stack_handle_t free_stack_handle;
};
+static int ref_tracker_cmp(void *priv, const struct list_head *a, const struct list_head *b)
+{
+ const struct ref_tracker *ta = list_entry(a, const struct ref_tracker, head);
+ const struct ref_tracker *tb = list_entry(b, const struct ref_tracker, head);
+
+ return ta->alloc_stack_handle - tb->alloc_stack_handle;
+}
+
void __ref_tracker_dir_print(struct ref_tracker_dir *dir,
unsigned int display_limit)
{
+ unsigned int i = 0, count = 0;
struct ref_tracker *tracker;
- unsigned int i = 0;
+ depot_stack_handle_t stack;
lockdep_assert_held(&dir->lock);
+ if (list_empty(&dir->list))
+ return;
+
+ list_sort(NULL, &dir->list, ref_tracker_cmp);
What is going to be the cost of sorting a list with 1,000,000 items in it ?
Do we really have such cases?
I just want to make sure we do not trade printing at most ~10 references
(from netdev_wait_allrefs()) to a soft lockup :/ with no useful info
if something went terribly wrong.
I suggest that you do not sort a potential big list, and instead
attempt to allocate an array of @display_limits 'struct stack_counts'
I suspect @display_limits will always be kept to a reasonable value
(less than 100 ?)
I though rather about 16 :)
In theory everything is possible, but do we have real case examples
which could lead to 100 stack traces?
Maybe some frameworks used by multiple consumers (drivers) ???
struct stack_counts {
depot_stack_handle_t stack_handle;
unsigned int count;
}
Then, iterating the list and update the array (that you can keep
sorted by ->stack_handle)
Then after iterating, print the (at_most) @display_limits handles
found in the temp array.
OK, could be faster and less invasive.
Other solution would be keeping the array in dir and update in every
tracker alloc/free, this way we avoid iteration over potentially big
list, but it would cost memory and since printing is rather rare I am
not sure if it is worth.
I will try your proposition.
Regards
Andrzej
+
list_for_each_entry(tracker, &dir->list, head) {
- if (i < display_limit) {
- pr_err("leaked reference.\n");
- if (tracker->alloc_stack_handle)
- stack_depot_print(tracker->alloc_stack_handle);
- i++;
- } else {
+ if (i++ >= display_limit)
break;
- }
+ if (!count++)
+ stack = tracker->alloc_stack_handle;
+ if (stack == tracker->alloc_stack_handle &&
+ !list_is_last(&tracker->head, &dir->list))
+ continue;
+
+ pr_err("leaked %d references.\n", count);
+ if (stack)
+ stack_depot_print(stack);
+ count = 0;
}
}
EXPORT_SYMBOL(__ref_tracker_dir_print);
--
2.25.1
