==================================================================
BUG: KASAN: use-after-free in atomic_fetch_add include/asm-generic/atomic-instrumented.h:111 [inline]
BUG: KASAN: use-after-free in refcount_add include/linux/refcount.h:188 [inline]
BUG: KASAN: use-after-free in refcount_inc include/linux/refcount.h:228 [inline]
BUG: KASAN: use-after-free in get_task_struct include/linux/sched/task.h:111 [inline]
BUG: KASAN: use-after-free in kthread_stop+0x32/0x460 kernel/kthread.c:612
Write of size 4 at addr ffff8881e1e94ee0 by task syz-executor.1/318

CPU: 1 PID: 318 Comm: syz-executor.1 Not tainted 5.4.219-syzkaller-00013-g4a947285bcca #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1d8/0x241 lib/dump_stack.c:118
 print_address_description+0x8c/0x630 mm/kasan/report.c:384
 __kasan_report+0xf6/0x130 mm/kasan/report.c:516
 kasan_report+0x30/0x60 mm/kasan/common.c:653
 check_memory_region_inline mm/kasan/generic.c:141 [inline]
 check_memory_region+0x298/0x2d0 mm/kasan/generic.c:191
 atomic_fetch_add include/asm-generic/atomic-instrumented.h:111 [inline]
 refcount_add include/linux/refcount.h:188 [inline]
 refcount_inc include/linux/refcount.h:228 [inline]
 get_task_struct include/linux/sched/task.h:111 [inline]
 kthread_stop+0x32/0x460 kernel/kthread.c:612
 ext4_put_super+0x789/0xbc0 fs/ext4/super.c:1055
 generic_shutdown_super+0x11b/0x2a0 fs/super.c:464
 kill_block_super+0x79/0xd0 fs/super.c:1444
 deactivate_locked_super+0xaf/0x100 fs/super.c:335
 deactivate_super+0x1b3/0x270 fs/super.c:366
 cleanup_mnt+0x432/0x4e0 fs/namespace.c:1102
 task_work_run+0x186/0x1b0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x1ba/0x1d0 arch/x86/entry/common.c:163
 prepare_exit_to_usermode+0x17c/0x1d0 arch/x86/entry/common.c:194
 entry_SYSCALL_64_after_hwframe+0x5c/0xc1

Allocated by task 2:
 save_stack mm/kasan/common.c:70 [inline]
 set_track mm/kasan/common.c:78 [inline]
 __kasan_kmalloc+0x131/0x1e0 mm/kasan/common.c:529
 slab_post_alloc_hook mm/slab.h:584 [inline]
 slab_alloc_node mm/slub.c:2829 [inline]
 slab_alloc mm/slub.c:2837 [inline]
 kmem_cache_alloc+0xd0/0x210 mm/slub.c:2842
 kmem_cache_alloc_node include/linux/slab.h:427 [inline]
 alloc_task_struct_node kernel/fork.c:171 [inline]
 dup_task_struct+0x4f/0x5a0 kernel/fork.c:871
 copy_process+0x56e/0x3230 kernel/fork.c:1878
 _do_fork+0x196/0x8d0 kernel/fork.c:2391
 kernel_thread+0x169/0x1d0 kernel/fork.c:2481
 create_kthread kernel/kthread.c:311 [inline]
 kthreadd+0x3cd/0x520 kernel/kthread.c:654
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:354

Freed by task 9:
 save_stack mm/kasan/common.c:70 [inline]
 set_track mm/kasan/common.c:78 [inline]
 kasan_set_free_info mm/kasan/common.c:345 [inline]
 __kasan_slab_free+0x178/0x240 mm/kasan/common.c:487
 slab_free_hook mm/slub.c:1455 [inline]
 slab_free_freelist_hook+0x80/0x150 mm/slub.c:1494
 slab_free mm/slub.c:3080 [inline]
 kmem_cache_free+0xa9/0x1d0 mm/slub.c:3096
 __rcu_reclaim kernel/rcu/rcu.h:222 [inline]
 rcu_do_batch+0x49e/0xa10 kernel/rcu/tree.c:2167
 rcu_core+0x4ba/0xca0 kernel/rcu/tree.c:2387
 __do_softirq+0x23e/0x643 kernel/softirq.c:292

The buggy address belongs to the object at ffff8881e1e94ec0
 which belongs to the cache task_struct of size 3904
The buggy address is located 32 bytes inside of
 3904-byte region [ffff8881e1e94ec0, ffff8881e1e95e00)
The buggy address belongs to the page:
page:ffffea000787a400 refcount:1 mapcount:0 mapping:ffff8881f5ceca00 index:0x0 compound_mapcount: 0
flags: 0x8000000000010200(slab|head)
raw: 8000000000010200 0000000000000000 0000000100000001 ffff8881f5ceca00
raw: 0000000000000000 0000000000080008 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC)
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook mm/page_alloc.c:2165 [inline]
 prep_new_page+0x194/0x380 mm/page_alloc.c:2171
 get_page_from_freelist+0x524/0x560 mm/page_alloc.c:3794
 __alloc_pages_nodemask+0x372/0x860 mm/page_alloc.c:4891
 alloc_slab_page+0x39/0x3e0 mm/slub.c:343
 allocate_slab mm/slub.c:1683 [inline]
 new_slab+0x97/0x450 mm/slub.c:1749
 new_slab_objects mm/slub.c:2505 [inline]
 ___slab_alloc+0x320/0x4a0 mm/slub.c:2667
 __slab_alloc+0x5a/0x90 mm/slub.c:2707
 slab_alloc_node mm/slub.c:2792 [inline]
 slab_alloc mm/slub.c:2837 [inline]
 kmem_cache_alloc+0x100/0x210 mm/slub.c:2842
 kmem_cache_alloc_node include/linux/slab.h:427 [inline]
 alloc_task_struct_node kernel/fork.c:171 [inline]
 dup_task_struct+0x4f/0x5a0 kernel/fork.c:871
 copy_process+0x56e/0x3230 kernel/fork.c:1878
 _do_fork+0x196/0x8d0 kernel/fork.c:2391
 __do_sys_clone kernel/fork.c:2549 [inline]
 __se_sys_clone kernel/fork.c:2530 [inline]
 __x64_sys_clone+0x287/0x2f0 kernel/fork.c:2530
 do_syscall_64+0xcb/0x1c0 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x5c/0xc1
page_owner free stack trace missing

Memory state around the buggy address:
 ffff8881e1e94d80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8881e1e94e00: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
>ffff8881e1e94e80: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                                       ^
 ffff8881e1e94f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881e1e94f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 318 at lib/refcount.c:25 refcount_warn_saturate+0x13d/0x1a0 lib/refcount.c:25
Modules linked in:
CPU: 1 PID: 318 Comm: syz-executor.1 Tainted: G    B             5.4.219-syzkaller-00013-g4a947285bcca #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
RIP: 0010:refcount_warn_saturate+0x13d/0x1a0 lib/refcount.c:25
Code: c7 e0 02 fe 84 31 c0 e8 91 76 15 ff 0f 0b eb a3 e8 78 9d 3e ff c6 05 08 27 fe 03 01 48 c7 c7 60 03 fe 84 31 c0 e8 73 76 15 ff <0f> 0b eb 85 e8 5a 9d 3e ff c6 05 eb 26 fe 03 01 48 c7 c7 c0 03 fe
RSP: 0018:ffff8881aae27c50 EFLAGS: 00010246
RAX: 01e4c7d253ad2900 RBX: 0000000000000002 RCX: ffff8881dd12de80
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 0000000000000002 R08: ffffffff814e3a77 R09: ffffed103edeaa08
R10: ffffed103edeaa08 R11: 1ffff1103edeaa07 R12: dffffc0000000000
R13: ffff8881e1e94ec0 R14: dffffc0000000000 R15: ffff8881e1e94ee0
FS:  000055555700c400(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555555e58728 CR3: 00000001aadac000 CR4: 00000000003406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 refcount_add include/linux/refcount.h:192 [inline]
 refcount_inc include/linux/refcount.h:228 [inline]
 get_task_struct include/linux/sched/task.h:111 [inline]
 kthread_stop+0x1a1/0x460 kernel/kthread.c:612
 ext4_put_super+0x789/0xbc0 fs/ext4/super.c:1055
 generic_shutdown_super+0x11b/0x2a0 fs/super.c:464
 kill_block_super+0x79/0xd0 fs/super.c:1444
 deactivate_locked_super+0xaf/0x100 fs/super.c:335
 deactivate_super+0x1b3/0x270 fs/super.c:366
 cleanup_mnt+0x432/0x4e0 fs/namespace.c:1102
 task_work_run+0x186/0x1b0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x1ba/0x1d0 arch/x86/entry/common.c:163
 prepare_exit_to_usermode+0x17c/0x1d0 arch/x86/entry/common.c:194
 entry_SYSCALL_64_after_hwframe+0x5c/0xc1
---[ end trace 378b03de9181acef ]---