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BUG: KCSAN: data-race in dd_insert_request / ll_back_merge_fn

write to 0xffff88810277e140 of 8 bytes by task 14150 on cpu 0:
 dd_insert_request+0x327/0x330 block/mq-deadline.c:510
 dd_insert_requests+0xfe/0x170 block/mq-deadline.c:533
 blk_mq_sched_insert_requests+0xbe/0x200 block/blk-mq-sched.c:488
 blk_mq_flush_plug_list+0x2f5/0x3c0 block/blk-mq.c:1954
 blk_flush_plug_list+0x235/0x260 block/blk-core.c:1747
 blk_finish_plug+0x44/0x60 block/blk-core.c:1764
 ext4_writepages+0x18a1/0x1d10 fs/ext4/inode.c:2851
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range mm/filemap.c:413 [inline]
 file_write_and_wait_range+0x180/0x210 mm/filemap.c:792
 ext4_sync_file+0x105/0x670 fs/ext4/fsync.c:151
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2982 [inline]
 ext4_buffered_write_iter+0x39c/0x3f0 fs/ext4/file.c:277
 ext4_file_write_iter+0x2e7/0x11d0 fs/ext4/file.c:519
 call_write_iter include/linux/fs.h:2114 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4c0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x40a/0x750 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:936
 splice_direct_to_actor+0x345/0x650 fs/splice.c:891
 do_splice_direct+0xf5/0x170 fs/splice.c:979
 do_sendfile+0x773/0xda0 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1325 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1311
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88810277e140 of 8 bytes by task 14141 on cpu 1:
 req_set_nomerge block/blk.h:251 [inline]
 ll_new_hw_segment block/blk-merge.c:576 [inline]
 ll_back_merge_fn+0x355/0x460 block/blk-merge.c:595
 bio_attempt_back_merge+0x35/0x3f0 block/blk-merge.c:937
 blk_attempt_bio_merge+0x229/0x270 block/blk-merge.c:1019
 blk_attempt_plug_merge+0xd1/0x130 block/blk-merge.c:1082
 blk_mq_submit_bio+0x13a/0xe90 block/blk-mq.c:2195
 __submit_bio_noacct_mq block/blk-core.c:1014 [inline]
 submit_bio_noacct+0x6f2/0x7e0 block/blk-core.c:1047
 submit_bio+0x16d/0x2b0 block/blk-core.c:1090
 iomap_dio_submit_bio fs/iomap/direct-io.c:76 [inline]
 iomap_dio_bio_actor+0x91d/0xb50 fs/iomap/direct-io.c:342
 iomap_dio_actor+0x26e/0x3b0 fs/iomap/direct-io.c:417
 iomap_apply+0x1e2/0x400 fs/iomap/apply.c:84
 __iomap_dio_rw+0x5af/0xad0 fs/iomap/direct-io.c:561
 iomap_dio_rw+0x30/0x70 fs/iomap/direct-io.c:649
 ext4_dio_write_iter fs/ext4/file.c:568 [inline]
 ext4_file_write_iter+0xa04/0x11d0 fs/ext4/file.c:678
 call_write_iter include/linux/fs.h:2114 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 14141 Comm: syz-executor.0 Not tainted 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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