mm, swap: ratelimit bad swap entry reports

A corrupt page table hands the same bogus entry to get_swap_device() on
every access to the mapping, and every rejection is logged.  One machine
logged 6185620 copies of the same line in a few hours.

swap_dup_entry_direct() prints the same message from the fork path, once
per call: the WARN_ON_ONCE() guarding it warns once, the pr_err() inside
does not.

Rate limit all three prints.

Link: https://lore.kernel.org/20260818-swap_part_one-v1-1-a4fc58119fc0@debian.org
Fixes: 23b230ba8ac3 ("mm/swap: print bad swap offset entry in get_swap_device")
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Kairui Song <kasong@tencent.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index dacef34..53bf01d 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1899,11 +1899,11 @@ struct swap_info_struct *get_swap_device(swp_entry_t entry)
 
        return si;
 bad_nofile:
-       pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val);
+       pr_err_ratelimited("%s: %s%08lx\n", __func__, Bad_file, entry.val);
 out:
        return NULL;
 put_out:
-       pr_err("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
+       pr_err_ratelimited("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
        percpu_ref_put(&si->users);
        return NULL;
 }
@@ -3883,7 +3883,7 @@ int swap_dup_entry_direct(swp_entry_t entry)
 
        si = swap_entry_to_info(entry);
        if (WARN_ON_ONCE(!si)) {
-               pr_err("%s%08lx\n", Bad_file, entry.val);
+               pr_err_ratelimited("%s%08lx\n", Bad_file, entry.val);
                return -EINVAL;
        }