[PATCH] ext4: kunit: extents-test: Fix percpu_counters list corruption

["Ritesh Harjani (IBM)" <ritesh.list@gmail.com>]

commit 82f80e2e3b23 ("ext4: add extent status cache support to kunit tests"),
added ext4_es_register_shrinker() in extents_kunit_init() function but
failed to add the unregister shrinker routine in extents_kunit_exit().

This could cause the following percpu_counters list corruption bug.

         ok 1 split unwrit extent to 2 extents and convert 1st half writ
  slab kmalloc-4k start c0000002007ff000 pointer offset 1448 size 4096
 list_add corruption. next->prev should be prev (c000000004bc9e60), but was 0000000000000000. (next=c0000002007ff5a8).
 ------------[ cut here ]------------
 kernel BUG at lib/list_debug.c:29!
cpu 0x2: Vector: 700 (Program Check) at [c000000241927a30]
    pc: c000000000f26ed0: __list_add_valid_or_report+0x120/0x164
    lr: c000000000f26ecc: __list_add_valid_or_report+0x11c/0x164
    sp: c000000241927cd0
   msr: 800000000282b033
  current = 0xc000000241215200
  paca    = 0xc0000003fffff300   irqmask: 0x03   irq_happened: 0x09
    pid   = 258, comm = kunit_try_catch
kernel BUG at lib/list_debug.c:29!
enter ? for help
 __percpu_counter_init_many+0x148/0x184
 ext4_es_register_shrinker+0x74/0x23c
 extents_kunit_init+0x100/0x308
 kunit_try_run_case+0x78/0x1f8
 kunit_generic_run_threadfn_adapter+0x40/0x70
 kthread+0x190/0x1a0
 start_kernel_thread+0x14/0x18
2:mon>

This happens because:

extents_kunit_init(test N):
  ext4_es_register_shrinker(sbi)
    percpu_counters_init() x 4; // this adds 4 list nodes to global percpu_counters list
      list_add(&fbc->list, &percpu_counters);
    shrinker_register();

extents_kunit_exit(test N):
  kfree(sbi);			// frees sbi w/o removing those 4 list nodes.
  				// So, those list node now becomes dangling pointers

extents_kunit_init(test N+1):
  kzalloc_obj(ext4_sb_info)	// allocator returns same page, but zeroed.
  ext4_es_register_shrinker(sbi)
    percpu_counters_init()
      list_add(&fbc->list, &percpu_counters);
        __list_add_valid(new, prev, next);
	next->prev != prev 		// list corruption bug detected, since next->prev = NULL

Fixes: 82f80e2e3b23 ("ext4: add extent status cache support to kunit tests")
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/ext4/extents-test.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/extents-test.c b/fs/ext4/extents-test.c
index 7c4690eb7dad..a6b3e6b592a5 100644
--- a/fs/ext4/extents-test.c
+++ b/fs/ext4/extents-test.c
@@ -142,8 +142,10 @@ static struct file_system_type ext_fs_type = {

 static void extents_kunit_exit(struct kunit *test)
 {
-	struct ext4_sb_info *sbi = k_ctx.k_ei->vfs_inode.i_sb->s_fs_info;
+	struct super_block *sb = k_ctx.k_ei->vfs_inode.i_sb;
+	struct ext4_sb_info *sbi = sb->s_fs_info;

+	ext4_es_unregister_shrinker(sbi);
 	kfree(sbi);
 	kfree(k_ctx.k_ei);
 	kfree(k_ctx.k_data);
--
2.53.0