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BUG: KCSAN: data-race in blk_mq_rq_ctx_init / blk_mq_rq_ctx_init

write to 0xffff88812a7e9d48 of 8 bytes by task 11072 on cpu 0:
 blk_mq_rq_ctx_init+0x4cd/0x5d0 block/blk-mq.c:346
 __blk_mq_alloc_request+0x2d0/0x2f0 block/blk-mq.c:402
 blk_mq_make_request+0x265/0x1070 block/blk-mq.c:2053
 do_make_request block/blk-core.c:1084 [inline]
 generic_make_request+0x240/0x5d0 block/blk-core.c:1156
 submit_bio+0x200/0x370 block/blk-core.c:1275
 iomap_dio_submit_bio fs/iomap/direct-io.c:75 [inline]
 iomap_dio_bio_actor+0x89d/0xad0 fs/iomap/direct-io.c:310
 iomap_dio_actor+0x1ec/0x340 fs/iomap/direct-io.c:385
 iomap_apply+0x1da/0x520 fs/iomap/apply.c:80
 iomap_dio_rw+0x501/0x8c0 fs/iomap/direct-io.c:501
 ext4_dio_write_iter fs/ext4/file.c:545 [inline]
 ext4_file_write_iter+0xda4/0x1010 fs/ext4/file.c:653
 call_write_iter include/linux/fs.h:1907 [inline]
 do_iter_readv_writev+0x321/0x3c0 fs/read_write.c:694
 do_iter_write+0x10e/0x470 fs/read_write.c:999
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1040
 iter_file_splice_write+0x41a/0x770 fs/splice.c:750
 do_splice_from fs/splice.c:846 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x562/0xb10 fs/read_write.c:1521
 __do_sys_sendfile64 fs/read_write.c:1582 [inline]
 __se_sys_sendfile64 fs/read_write.c:1568 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1568
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812a7e9d48 of 8 bytes by task 11065 on cpu 1:
 blk_mq_rq_ctx_init+0x4bb/0x5d0 block/blk-mq.c:346
 __blk_mq_alloc_request+0x2d0/0x2f0 block/blk-mq.c:402
 blk_mq_make_request+0x265/0x1070 block/blk-mq.c:2053
 do_make_request block/blk-core.c:1084 [inline]
 generic_make_request+0x240/0x5d0 block/blk-core.c:1156
 submit_bio+0x200/0x370 block/blk-core.c:1275
 submit_bh_wbc+0x397/0x3d0 fs/buffer.c:3073
 submit_bh fs/buffer.c:3079 [inline]
 write_dirty_buffer+0xd4/0xe0 fs/buffer.c:3147
 fsync_buffers_list fs/buffer.c:731 [inline]
 sync_mapping_buffers+0x29e/0x7d0 fs/buffer.c:549
 ext4_fsync_nojournal fs/ext4/fsync.c:86 [inline]
 ext4_sync_file+0x25e/0x6e0 fs/ext4/fsync.c:170
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2882 [inline]
 iomap_dio_complete+0x2de/0x380 fs/iomap/direct-io.c:125
 iomap_dio_rw+0x874/0x8c0 fs/iomap/direct-io.c:572
 ext4_dio_write_iter fs/ext4/file.c:545 [inline]
 ext4_file_write_iter+0xda4/0x1010 fs/ext4/file.c:653
 call_write_iter include/linux/fs.h:1907 [inline]
 do_iter_readv_writev+0x321/0x3c0 fs/read_write.c:694
 do_iter_write+0x10e/0x470 fs/read_write.c:999
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1040
 iter_file_splice_write+0x41a/0x770 fs/splice.c:750
 do_splice_from fs/splice.c:846 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x562/0xb10 fs/read_write.c:1521
 __do_sys_sendfile64 fs/read_write.c:1582 [inline]
 __se_sys_sendfile64 fs/read_write.c:1568 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1568
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 11065 Comm: syz-executor.2 Not tainted 5.8.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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