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BUG: KCSAN: data-race in dd_insert_request / ll_back_merge_fn

write to 0xffff8881026f2140 of 8 bytes by task 20447 on cpu 1:
 dd_insert_request+0x327/0x330 block/mq-deadline.c:511
 dd_insert_requests+0xfe/0x170 block/mq-deadline.c:534
 blk_mq_sched_insert_request+0x237/0x280 block/blk-mq-sched.c:458
 blk_mq_submit_bio+0x518/0xdd0 block/blk-mq.c:2259
 __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
 submit_bh_wbc+0x2f3/0x330 fs/buffer.c:3075
 submit_bh fs/buffer.c:3081 [inline]
 __sync_dirty_buffer+0x136/0x1e0 fs/buffer.c:3176
 sync_dirty_buffer+0x16/0x20 fs/buffer.c:3189
 __ext4_handle_dirty_metadata+0x1d3/0x590 fs/ext4/ext4_jbd2.c:364
 ext4_free_data+0x258/0x2b0 fs/ext4/indirect.c:966
 ext4_free_branches+0x64/0x420 fs/ext4/indirect.c:1095
 ext4_free_branches+0x21b/0x420 fs/ext4/indirect.c:1030
 ext4_free_branches+0x21b/0x420 fs/ext4/indirect.c:1030
 ext4_ind_truncate+0x7c2/0x880 fs/ext4/indirect.c:1188
 ext4_truncate+0x756/0xa80 fs/ext4/inode.c:4264
 ext4_setattr+0xacc/0xec0 fs/ext4/inode.c:5504
 notify_change+0x8a3/0xa80 fs/attr.c:398
 do_truncate+0xe8/0x130 fs/open.c:64
 handle_truncate fs/namei.c:3017 [inline]
 do_open fs/namei.c:3365 [inline]
 path_openat+0x1a79/0x20b0 fs/namei.c:3494
 do_filp_open+0xd9/0x1f0 fs/namei.c:3521
 do_sys_openat2+0xa3/0x250 fs/open.c:1187
 do_sys_open fs/open.c:1203 [inline]
 __do_sys_openat fs/open.c:1219 [inline]
 __se_sys_openat fs/open.c:1214 [inline]
 __x64_sys_openat+0xef/0x110 fs/open.c:1214
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881026f2140 of 8 bytes by task 20456 on cpu 0:
 req_set_nomerge block/blk.h:251 [inline]
 ll_back_merge_fn+0x2b3/0x460 block/blk-merge.c:591
 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+0x13f/0xdd0 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+0xa4f/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: 0 PID: 20456 Comm: syz-executor.0 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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