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BUG: KASAN: use-after-free in relay_switch_subbuf+0x8c0/0x930 kernel/relay.c:755
Read of size 8 at addr ffff88803b0941b8 by task kworker/1:1/27873

CPU: 1 PID: 27873 Comm: kworker/1:1 Not tainted 5.1.0-rc7+ #99
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+0x7c/0x20d mm/kasan/report.c:187
 kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
 relay_switch_subbuf+0x8c0/0x930 kernel/relay.c:755
 relay_flush kernel/relay.c:883 [inline]
 relay_flush+0x1c4/0x280 kernel/relay.c:867
 __blk_trace_startstop.isra.0+0x216/0x630 kernel/trace/blktrace.c:668
 blk_trace_shutdown+0x5f/0x90 kernel/trace/blktrace.c:752
 __blk_release_queue+0x1dc/0x3a0 block/blk-sysfs.c:866
 process_one_work+0x98e/0x1790 kernel/workqueue.c:2269
 worker_thread+0x98/0xe40 kernel/workqueue.c:2415
 kthread+0x357/0x430 kernel/kthread.c:253
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352

Allocated by task 32040:
 save_stack+0x45/0xd0 mm/kasan/common.c:75
 set_track mm/kasan/common.c:87 [inline]
 __kasan_kmalloc mm/kasan/common.c:497 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:470
 kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:505
 slab_post_alloc_hook mm/slab.h:437 [inline]
 slab_alloc mm/slab.c:3393 [inline]
 kmem_cache_alloc+0x11a/0x6f0 mm/slab.c:3555
 __d_alloc+0x2e/0x8c0 fs/dcache.c:1622
 d_alloc+0x4d/0x2b0 fs/dcache.c:1701
 d_alloc_parallel+0xf4/0x1bc0 fs/dcache.c:2449
 __lookup_slow+0x1ab/0x500 fs/namei.c:1652
 lookup_one_len+0x16d/0x1a0 fs/namei.c:2541
 start_creating fs/debugfs/inode.c:313 [inline]
 start_creating+0xbf/0x1e0 fs/debugfs/inode.c:289
 __debugfs_create_file+0x65/0x400 fs/debugfs/inode.c:352
 debugfs_create_file+0x5a/0x70 fs/debugfs/inode.c:405
 blk_create_buf_file_callback+0x33/0x40 kernel/trace/blktrace.c:444
 relay_create_buf_file+0xfb/0x180 kernel/relay.c:428
 relay_open_buf.part.0+0x773/0xb60 kernel/relay.c:457
 relay_open_buf kernel/relay.c:449 [inline]
 relay_open kernel/relay.c:599 [inline]
 relay_open+0x523/0x980 kernel/relay.c:563
 do_blk_trace_setup+0x414/0xb90 kernel/trace/blktrace.c:532
 __blk_trace_setup+0xe3/0x190 kernel/trace/blktrace.c:577
 blk_trace_ioctl+0x170/0x300 kernel/trace/blktrace.c:716
 blkdev_ioctl+0x276/0x1d10 block/ioctl.c:591
 block_ioctl+0xee/0x130 fs/block_dev.c:1934
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0xd6e/0x1390 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+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 32029:
 save_stack+0x45/0xd0 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:3499 [inline]
 kmem_cache_free+0x86/0x260 mm/slab.c:3765
 __d_free+0x20/0x30 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+0x916/0x13a0 kernel/rcu/tree.c:2769
 __do_softirq+0x266/0x95a kernel/softirq.c:293

The buggy address belongs to the object at ffff88803b094160
 which belongs to the cache dentry(17:syz0) of size 288
The buggy address is located 88 bytes inside of
 288-byte region [ffff88803b094160, ffff88803b094280)
The buggy address belongs to the page:
page:ffffea0000ec2500 count:1 mapcount:0 mapping:ffff88808ed95d80 index:0x0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0000f765c8 ffffea0000f7bf08 ffff88808ed95d80
raw: 0000000000000000 ffff88803b094000 000000010000000b ffff8880610d85c0
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff8880610d85c0

Memory state around the buggy address:
 ffff88803b094080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88803b094100: fb fb fb fb fc fc fc fc fc fc fc fc fb fb fb fb
>ffff88803b094180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                        ^
 ffff88803b094200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88803b094280: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
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