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BUG: KASAN: use-after-free in relay_switch_subbuf+0x8be/0x920 kernel/relay.c:755
Read of size 8 at addr ffff888092bf54f8 by task ksoftirqd/0/9

CPU: 0 PID: 9 Comm: ksoftirqd/0 Not tainted 5.3.0-rc4 #126
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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+0x12/0x17 mm/kasan/common.c:612
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
 relay_switch_subbuf+0x8be/0x920 kernel/relay.c:755
 relay_reserve include/linux/relay.h:261 [inline]
 trace_note.isra.0+0x5b8/0x6e0 kernel/trace/blktrace.c:93
 trace_note_tsk kernel/trace/blktrace.c:124 [inline]
 __blk_add_trace+0xb70/0xe10 kernel/trace/blktrace.c:264
 blk_add_trace_rq+0x185/0x1f0 kernel/trace/blktrace.c:813
 blk_add_trace_rq_complete+0x17a/0x1e0 kernel/trace/blktrace.c:842
 trace_block_rq_complete include/trace/events/block.h:116 [inline]
 blk_update_request+0x851/0xc10 block/blk-core.c:1403
 blk_mq_end_request+0x5b/0x560 block/blk-mq.c:557
 lo_complete_rq+0x210/0x2e0 drivers/block/loop.c:485
 blk_done_softirq+0x2fe/0x4d0 block/blk-softirq.c:37
 __do_softirq+0x262/0x98c kernel/softirq.c:292
 run_ksoftirqd kernel/softirq.c:603 [inline]
 run_ksoftirqd+0x8e/0x110 kernel/softirq.c:595
 smpboot_thread_fn+0x6a3/0xa40 kernel/smpboot.c:165
 kthread+0x361/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 24041:
 save_stack+0x23/0x90 mm/kasan/common.c:69
 set_track mm/kasan/common.c:77 [inline]
 __kasan_kmalloc mm/kasan/common.c:487 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:460
 kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:495
 slab_post_alloc_hook mm/slab.h:520 [inline]
 slab_alloc mm/slab.c:3319 [inline]
 kmem_cache_alloc+0x121/0x710 mm/slab.c:3483
 __d_alloc+0x2e/0x8c0 fs/dcache.c:1688
 d_alloc+0x4d/0x280 fs/dcache.c:1767
 __lookup_hash+0xcd/0x190 fs/namei.c:1540
 filename_create+0x1a7/0x4f0 fs/namei.c:3635
 user_path_create fs/namei.c:3692 [inline]
 do_symlinkat+0xf3/0x290 fs/namei.c:4147
 __do_sys_symlink fs/namei.c:4173 [inline]
 __se_sys_symlink fs/namei.c:4171 [inline]
 __x64_sys_symlink+0x59/0x80 fs/namei.c:4171
 do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:296
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9:
 save_stack+0x23/0x90 mm/kasan/common.c:69
 set_track mm/kasan/common.c:77 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:449
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:457
 __cache_free mm/slab.c:3425 [inline]
 kmem_cache_free+0x86/0x320 mm/slab.c:3693
 __d_free+0x20/0x30 fs/dcache.c:271
 __rcu_reclaim kernel/rcu/rcu.h:222 [inline]
 rcu_do_batch kernel/rcu/tree.c:2114 [inline]
 rcu_core+0x67f/0x1580 kernel/rcu/tree.c:2314
 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2323
 __do_softirq+0x262/0x98c kernel/softirq.c:292

The buggy address belongs to the object at ffff888092bf54a0
 which belongs to the cache dentry(87:syz4) of size 288
The buggy address is located 88 bytes inside of
 288-byte region [ffff888092bf54a0, ffff888092bf55c0)
The buggy address belongs to the page:
page:ffffea00024afd40 refcount:1 mapcount:0 mapping:ffff88808cd5d8c0 index:0xffff888092bf5600
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0002537fc8 ffffea00024aa7c8 ffff88808cd5d8c0
raw: ffff888092bf5600 ffff888092bf5080 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888092bf5380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888092bf5400: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>ffff888092bf5480: fc fc fc fc fb fb fb fb fb fb fb fb fb fb fb fb
                                                                ^
 ffff888092bf5500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888092bf5580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
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