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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) --- 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