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BUG: KASAN: use-after-free in disk_unblock_events+0x4b/0x50 block/genhd.c:1644
Read of size 8 at addr ffff8881cdfd2768 by task syz-executor768/28194

CPU: 1 PID: 28194 Comm: syz-executor768 Not tainted 4.14.134+ #19
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xca/0x134 lib/dump_stack.c:53
 print_address_description+0x60/0x226 mm/kasan/report.c:187
 __kasan_report.cold+0x1a/0x41 mm/kasan/report.c:316

Allocated by task 28164:
 save_stack mm/kasan/common.c:76 [inline]
 set_track mm/kasan/common.c:85 [inline]
 __kasan_kmalloc.part.0+0x53/0xc0 mm/kasan/common.c:495
 kmem_cache_alloc_node_trace include/linux/slab.h:378 [inline]
 kmalloc_node include/linux/slab.h:526 [inline]
 kzalloc_node include/linux/slab.h:672 [inline]
 alloc_disk_node+0x5b/0x3d0 block/genhd.c:1387
 0xffffffffffffffff

Freed by task 28194:
 save_stack mm/kasan/common.c:76 [inline]
 set_track mm/kasan/common.c:85 [inline]
 __kasan_slab_free+0x164/0x210 mm/kasan/common.c:457
 slab_free_hook mm/slub.c:1403 [inline]
 slab_free_freelist_hook mm/slub.c:1430 [inline]
 slab_free mm/slub.c:3005 [inline]
 kfree+0xfa/0x320 mm/slub.c:3942
 device_release+0xf4/0x1a0 drivers/base/core.c:822
 0xffffffffffffffff

The buggy address belongs to the object at ffff8881cdfd2200
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1384 bytes inside of
 2048-byte region [ffff8881cdfd2200, ffff8881cdfd2a00)
The buggy address belongs to the page:
page:ffffea000737f400 count:1 mapcount:0 mapping:          (null) index:0xffff8881cdfd3300 compound_mapcount: 0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 0000000000000000 ffff8881cdfd3300 00000001800f000e
raw: ffffea000759c400 0000000200000002 ffff8881da802800 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881cdfd2600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881cdfd2680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881cdfd2700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                          ^
 ffff8881cdfd2780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881cdfd2800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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