overlayfs: missing 'lowerdir'
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BUG: KCSAN: data-race in relay_switch_subbuf / relay_switch_subbuf

write to 0xffff8880b2f56c38 of 8 bytes by task 19960 on cpu 1:
 relay_switch_subbuf+0x478/0x490 kernel/relay.c:790
 relay_reserve include/linux/relay.h:261 [inline]
 __blk_add_trace+0x801/0x840 kernel/trace/blktrace.c:272
 blk_add_trace_rq+0x15b/0x1a0 kernel/trace/blktrace.c:813
 blk_add_trace_rq_insert+0xec/0x100 kernel/trace/blktrace.c:820
 trace_block_rq_insert include/trace/events/block.h:192 [inline]
 blk_mq_sched_request_inserted+0xf2/0x140 block/blk-mq-sched.c:356
 dd_insert_request block/mq-deadline.c:499 [inline]
 dd_insert_requests+0x1f1/0x5a0 block/mq-deadline.c:535
 blk_mq_sched_insert_request+0x266/0x3f0 block/blk-mq-sched.c:401
 blk_mq_make_request+0x78b/0xf60 block/blk-mq.c:2048
 generic_make_request block/blk-core.c:1064 [inline]
 generic_make_request+0x196/0x740 block/blk-core.c:1006
 submit_bio+0x96/0x3c0 block/blk-core.c:1190
 submit_bh_wbc+0x40f/0x460 fs/buffer.c:3095
 submit_bh fs/buffer.c:3101 [inline]
 __sync_dirty_buffer+0xd3/0x210 fs/buffer.c:3187
 sync_dirty_buffer+0x24/0x40 fs/buffer.c:3200
 ext4_write_inode+0x312/0x330 fs/ext4/inode.c:5427
 write_inode fs/fs-writeback.c:1309 [inline]
 __writeback_single_inode+0x6f7/0x8e0 fs/fs-writeback.c:1508
 writeback_single_inode+0x232/0x310 fs/fs-writeback.c:1562
 sync_inode fs/fs-writeback.c:2599 [inline]
 sync_inode_metadata+0x74/0xa0 fs/fs-writeback.c:2619
 __generic_file_fsync+0x122/0x190 fs/libfs.c:1011
 ext4_sync_file+0x48e/0xb00 fs/ext4/fsync.c:120
 vfs_fsync_range+0x82/0x150 fs/sync.c:197
 generic_write_sync include/linux/fs.h:2853 [inline]
 ext4_file_write_iter+0x45b/0xa00 fs/ext4/file.c:279
 call_write_iter include/linux/fs.h:1895 [inline]
 do_iter_readv_writev+0x487/0x5b0 fs/read_write.c:693
 do_iter_write fs/read_write.c:970 [inline]
 do_iter_write+0x13b/0x3c0 fs/read_write.c:951
 vfs_iter_write+0x5c/0x80 fs/read_write.c:983
 iter_file_splice_write+0x4c0/0x7f0 fs/splice.c:746
 do_splice_from fs/splice.c:848 [inline]
 direct_splice_actor+0xa0/0xc0 fs/splice.c:1020
 splice_direct_to_actor+0x215/0x510 fs/splice.c:975
 do_splice_direct+0x161/0x1e0 fs/splice.c:1063
 do_sendfile+0x384/0x7f0 fs/read_write.c:1464
 __do_sys_sendfile64 fs/read_write.c:1519 [inline]
 __se_sys_sendfile64 fs/read_write.c:1511 [inline]
 __x64_sys_sendfile64+0xbe/0x140 fs/read_write.c:1511
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8880b2f56c38 of 8 bytes by task 19959 on cpu 0:
 relay_switch_subbuf+0x478/0x490 kernel/relay.c:790
 relay_reserve include/linux/relay.h:261 [inline]
 __blk_add_trace+0x801/0x840 kernel/trace/blktrace.c:272
 blk_add_trace_plug+0x54/0x70 kernel/trace/blktrace.c:941
 trace_block_plug include/trace/events/block.h:456 [inline]
 blk_mq_make_request+0x931/0xf60 block/blk-mq.c:2008
 generic_make_request block/blk-core.c:1064 [inline]
 generic_make_request+0x196/0x740 block/blk-core.c:1006
 submit_bio+0x96/0x3c0 block/blk-core.c:1190
 submit_bh_wbc+0x40f/0x460 fs/buffer.c:3095
 submit_bh fs/buffer.c:3101 [inline]
 write_dirty_buffer fs/buffer.c:3169 [inline]
 write_dirty_buffer+0x83/0x100 fs/buffer.c:3160
 fsync_buffers_list fs/buffer.c:705 [inline]
 sync_mapping_buffers+0x2a0/0x6e0 fs/buffer.c:523
 ext4_sync_parent fs/ext4/fsync.c:72 [inline]
 ext4_sync_file+0x82e/0xb00 fs/ext4/fsync.c:122
 vfs_fsync_range+0x82/0x150 fs/sync.c:197
 generic_write_sync include/linux/fs.h:2853 [inline]
 ext4_file_write_iter+0x45b/0xa00 fs/ext4/file.c:279
 call_write_iter include/linux/fs.h:1895 [inline]
 new_sync_write+0x388/0x4a0 fs/read_write.c:483
 __vfs_write+0xb1/0xc0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0xd5/0x1b0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 19959 Comm: syz-executor.0 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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