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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 ffff8881a2692fe8 by task syz-executor.0/1851

CPU: 0 PID: 1851 Comm: syz-executor.0 Not tainted 4.14.129+ #11
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xb9/0x10e lib/dump_stack.c:53
 print_address_description+0x60/0x226 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report mm/kasan/report.c:409 [inline]
 kasan_report.cold+0xae/0x2d5 mm/kasan/report.c:393

Allocated by task 14968:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc.part.0+0x4f/0xd0 mm/kasan/kasan.c:551
 kmem_cache_alloc_trace+0x126/0x310 mm/slub.c:2750
 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

Freed by task 1851:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0xb0/0x190 mm/kasan/kasan.c:524
 slab_free_hook mm/slub.c:1389 [inline]
 slab_free_freelist_hook mm/slub.c:1410 [inline]
 slab_free mm/slub.c:2966 [inline]
 kfree+0xf5/0x310 mm/slub.c:3897
 device_release+0xf4/0x1a0 drivers/base/core.c:822

The buggy address belongs to the object at ffff8881a2692a80
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1384 bytes inside of
 2048-byte region [ffff8881a2692a80, ffff8881a2693280)
The buggy address belongs to the page:
page:ffffea000689a400 count:1 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 0000000000000000 0000000000000000 00000001800f000f
raw: dead000000000100 dead000000000200 ffff8881da802800 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881a2692e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881a2692f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881a2692f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                          ^
 ffff8881a2693000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881a2693080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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