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BUG: KCSAN: data-race in blk_mq_get_request / blk_mq_get_request

write to 0xffff88812a20c148 of 8 bytes by task 12366 on cpu 0:
 blk_mq_get_request+0x8e1/0xb50 block/blk-mq.c:418
 blk_mq_make_request+0x2d9/0xf60 block/blk-mq.c:1974
 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]
 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_writev+0x118/0x1c0 fs/read_write.c:1015
 do_pwritev+0x131/0x1d0 fs/read_write.c:1112
 __do_sys_pwritev fs/read_write.c:1159 [inline]
 __se_sys_pwritev fs/read_write.c:1154 [inline]
 __x64_sys_pwritev+0x61/0x80 fs/read_write.c:1154
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812a20c148 of 8 bytes by task 12369 on cpu 1:
 blk_mq_get_request+0x8ce/0xb50 block/blk-mq.c:418
 blk_mq_make_request+0x2d9/0xf60 block/blk-mq.c:1974
 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]
 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_writev+0x118/0x1c0 fs/read_write.c:1015
 do_pwritev+0x131/0x1d0 fs/read_write.c:1112
 __do_sys_pwritev fs/read_write.c:1159 [inline]
 __se_sys_pwritev fs/read_write.c:1154 [inline]
 __x64_sys_pwritev+0x61/0x80 fs/read_write.c:1154
 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: 1 PID: 12369 Comm: syz-executor.4 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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