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BUG: KASAN: use-after-free in blk_mq_free_rqs+0x49f/0x4b0 block/blk-mq.c:2049
Read of size 8 at addr ffff8880a3edef90 by task kworker/0:5/8874

CPU: 0 PID: 8874 Comm: kworker/0:5 Not tainted 5.2.0-rc3-next-20190607 #11
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events __blk_release_queue
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 print_address_description.cold+0xd4/0x306 mm/kasan/report.c:351
 __kasan_report.cold+0x1b/0x36 mm/kasan/report.c:482
 kasan_report+0x12/0x20 mm/kasan/common.c:614
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
 blk_mq_free_rqs+0x49f/0x4b0 block/blk-mq.c:2049
 blk_mq_sched_free_tags block/blk-mq-sched.c:453 [inline]
 blk_mq_sched_tags_teardown+0x126/0x210 block/blk-mq-sched.c:485
 blk_mq_exit_sched+0x1fa/0x2d0 block/blk-mq-sched.c:557
 elevator_exit+0x70/0xa0 block/elevator.c:185
 blk_exit_queue block/blk-sysfs.c:853 [inline]
 __blk_release_queue+0x127/0x330 block/blk-sysfs.c:895
 process_one_work+0x989/0x1790 kernel/workqueue.c:2269
 worker_thread+0x98/0xe40 kernel/workqueue.c:2415
 kthread+0x354/0x420 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 1:
 save_stack+0x23/0x90 mm/kasan/common.c:71
 set_track mm/kasan/common.c:79 [inline]
 __kasan_kmalloc mm/kasan/common.c:489 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
 kmem_cache_alloc_trace+0x151/0x750 mm/slab.c:3549
 kmalloc include/linux/slab.h:547 [inline]
 kzalloc include/linux/slab.h:742 [inline]
 loop_add+0x51/0x8d0 drivers/block/loop.c:1973
 loop_init+0x1fe/0x25a drivers/block/loop.c:2267
 do_one_initcall+0x107/0x7ba init/main.c:915
 do_initcall_level init/main.c:983 [inline]
 do_initcalls init/main.c:991 [inline]
 do_basic_setup init/main.c:1009 [inline]
 kernel_init_freeable+0x4d4/0x5c3 init/main.c:1169
 kernel_init+0x12/0x1c5 init/main.c:1087
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Freed by task 21423:
 save_stack+0x23/0x90 mm/kasan/common.c:71
 set_track mm/kasan/common.c:79 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x106/0x2a0 mm/slab.c:3753
 loop_remove+0xa1/0xd0 drivers/block/loop.c:2078
 loop_control_ioctl drivers/block/loop.c:2173 [inline]
 loop_control_ioctl+0x320/0x360 drivers/block/loop.c:2139
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:696
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
 do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a3eded80
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 528 bytes inside of
 1024-byte region [ffff8880a3eded80, ffff8880a3edf180)
The buggy address belongs to the page:
page:ffffea00028fb780 refcount:1 mapcount:0 mapping:ffff8880aa400ac0 index:0xffff8880a3edf680 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea000269d208 ffffea0002a65a08 ffff8880aa400ac0
raw: ffff8880a3edf680 ffff8880a3ede000 0000000100000005 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a3edee80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a3edef00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880a3edef80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff8880a3edf000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a3edf080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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