The comparison function cmp_loc_by_count() used for sorting stack trace locations in debugfs currently returns -1 if a->count > b->count and 1 otherwise. This breaks the antisymmetry property required by sort(), because when two counts are equal, both cmp(a, b) and cmp(b, a) return 1. This can lead to undefined or incorrect ordering results. Fix it by updating the comparison logic to explicitly handle the case when counts are equal, and use cmp_int() to ensure the comparison function adheres to the required mathematical properties of antisymmetry. Fixes: 553c0369b3e1 ("mm/slub: sort debugfs output by frequency of stack traces") Reviewed-by: Joshua Hahn Signed-off-by: Kuan-Wei Chiu --- mm/slub.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 30003763d224..081816ff89ab 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -7716,10 +7716,7 @@ static int cmp_loc_by_count(const void *a, const void *b, const void *data) struct location *loc1 = (struct location *)a; struct location *loc2 = (struct location *)b; - if (loc1->count > loc2->count) - return -1; - else - return 1; + return cmp_int(loc2->count, loc1->count); } static void *slab_debugfs_start(struct seq_file *seq, loff_t *ppos) -- 2.34.1 The comparison function used to sort stack trace locations in debugfs never relied on the third argument. Therefore, sort_r() is unnecessary. Switch to sort() with a two-argument comparison function to keep the code simple and aligned with the intended usage. Signed-off-by: Kuan-Wei Chiu --- mm/slub.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 081816ff89ab..39a238384892 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -7711,7 +7711,7 @@ static void *slab_debugfs_next(struct seq_file *seq, void *v, loff_t *ppos) return NULL; } -static int cmp_loc_by_count(const void *a, const void *b, const void *data) +static int cmp_loc_by_count(const void *a, const void *b) { struct location *loc1 = (struct location *)a; struct location *loc2 = (struct location *)b; @@ -7778,8 +7778,8 @@ static int slab_debug_trace_open(struct inode *inode, struct file *filep) } /* Sort locations by count */ - sort_r(t->loc, t->count, sizeof(struct location), - cmp_loc_by_count, NULL, NULL); + sort(t->loc, t->count, sizeof(struct location), + cmp_loc_by_count, NULL); bitmap_free(obj_map); return 0; -- 2.34.1