==================================================================
BUG: KASAN: use-after-free in relay_switch_subbuf+0xb0d/0xc40 kernel/relay.c:755
Read of size 8 at addr ffff8880a6f62bd8 by task kworker/0:1/28244

CPU: 0 PID: 28244 Comm: kworker/0:1 Not tainted 5.1.0-rc2+ #0
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+0x113/0x167 lib/dump_stack.c:113
 print_address_description.cold.5+0x9/0x1ff mm/kasan/report.c:187
 kasan_report.cold.6+0x1b/0x39 mm/kasan/report.c:317
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
 relay_switch_subbuf+0xb0d/0xc40 kernel/relay.c:755
 relay_flush+0x183/0x230 kernel/relay.c:883
 __blk_trace_startstop.isra.20+0x3f9/0x540 kernel/trace/blktrace.c:668
 blk_trace_shutdown+0x4c/0x70 kernel/trace/blktrace.c:752
 __blk_release_queue+0x17a/0x310 block/blk-sysfs.c:866
 process_one_work+0x830/0x16a0 kernel/workqueue.c:2269
 worker_thread+0x85/0xb60 kernel/workqueue.c:2415
 kthread+0x324/0x3e0 kernel/kthread.c:253
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 28621:
 save_stack+0x43/0xd0 mm/kasan/common.c:75
 set_track mm/kasan/common.c:87 [inline]
 __kasan_kmalloc.constprop.9+0xc7/0xd0 mm/kasan/common.c:497
 kasan_slab_alloc+0x12/0x20 mm/kasan/common.c:505
 slab_post_alloc_hook mm/slab.h:436 [inline]
 slab_alloc mm/slab.c:3392 [inline]
 kmem_cache_alloc+0x11a/0x720 mm/slab.c:3554
 __d_alloc+0x28/0x8a0 fs/dcache.c:1622
 d_alloc+0x43/0x260 fs/dcache.c:1701
 d_alloc_parallel+0xf3/0x1750 fs/dcache.c:2449
 __lookup_slow+0x18d/0x400 fs/namei.c:1652
 lookup_one_len+0x132/0x160 fs/namei.c:2541
 start_creating+0x91/0x190 fs/debugfs/inode.c:308
 __debugfs_create_file+0x33/0x390 fs/debugfs/inode.c:347
 debugfs_create_file+0x24/0x30 fs/debugfs/inode.c:400
 blk_create_buf_file_callback+0x19/0x20 kernel/trace/blktrace.c:444
 relay_create_buf_file+0xea/0x160 kernel/relay.c:428
 relay_open_buf.part.10+0x614/0xa00 kernel/relay.c:457
 relay_open_buf kernel/relay.c:449 [inline]
 relay_open+0x48f/0x890 kernel/relay.c:599
 do_blk_trace_setup+0x3b5/0xa70 kernel/trace/blktrace.c:532
 __blk_trace_setup+0xb4/0x130 kernel/trace/blktrace.c:577
 blk_trace_ioctl+0x155/0x2a0 kernel/trace/blktrace.c:716
 blkdev_ioctl+0x7a2/0x1830 block/ioctl.c:591
 block_ioctl+0xd7/0x130 fs/block_dev.c:1933
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0x196/0x10c0 fs/ioctl.c:696
 ksys_ioctl+0x62/0x90 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:718
 do_syscall_64+0xd0/0x4d0 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 0:
 save_stack+0x43/0xd0 mm/kasan/common.c:75
 set_track mm/kasan/common.c:87 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:459
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:467
 __cache_free mm/slab.c:3498 [inline]
 kmem_cache_free+0x83/0x290 mm/slab.c:3764
 __d_free+0x17/0x20 fs/dcache.c:269
 __rcu_reclaim kernel/rcu/rcu.h:227 [inline]
 rcu_do_batch kernel/rcu/tree.c:2475 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2788 [inline]
 rcu_core+0x8f4/0x12e0 kernel/rcu/tree.c:2769
 __do_softirq+0x260/0x958 kernel/softirq.c:293

The buggy address belongs to the object at ffff8880a6f62b80
 which belongs to the cache dentry of size 288
The buggy address is located 88 bytes inside of
 288-byte region [ffff8880a6f62b80, ffff8880a6f62ca0)
The buggy address belongs to the page:
page:ffffea00029bd880 count:1 mapcount:0 mapping:ffff88821bc45200 index:0x0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0002577b08 ffffea00022c0608 ffff88821bc45200
raw: 0000000000000000 ffff8880a6f62080 000000010000000b 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a6f62a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a6f62b00: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff8880a6f62b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                    ^
 ffff8880a6f62c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a6f62c80: fb fb fb fb fc fc fc fc fc fc fc fc 00 00 00 00
==================================================================