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BUG: KCSAN: data-race in blk_mq_get_request / blk_mq_get_request

read to 0xffff888129931d48 of 8 bytes by task 15258 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]
 __sync_dirty_buffer+0xd3/0x210 fs/buffer.c:3187
 sync_dirty_buffer+0x24/0x40 fs/buffer.c:3200
 __ext4_handle_dirty_metadata+0x19c/0x350 fs/ext4/ext4_jbd2.c:300
 ext4_handle_dirty_dirblock+0x20a/0x280 fs/ext4/namei.c:404
 ext4_delete_entry+0x266/0x2c0 fs/ext4/namei.c:2509
 ext4_unlink fs/ext4/namei.c:3190 [inline]
 ext4_unlink+0x33f/0x7d0 fs/ext4/namei.c:3140
 vfs_unlink+0x225/0x3e0 fs/namei.c:3991
 do_unlinkat+0x32b/0x530 fs/namei.c:4055
 __do_sys_unlink fs/namei.c:4102 [inline]
 __se_sys_unlink fs/namei.c:4100 [inline]
 __x64_sys_unlink+0x3b/0x50 fs/namei.c:4100
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888129931d48 of 8 bytes by task 16038 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]
 __sync_dirty_buffer+0xd3/0x210 fs/buffer.c:3187
 sync_dirty_buffer+0x24/0x40 fs/buffer.c:3200
 __ext4_handle_dirty_metadata+0x19c/0x350 fs/ext4/ext4_jbd2.c:300
 ext4_handle_dirty_dirblock+0x20a/0x280 fs/ext4/namei.c:404
 add_dirent_to_buf+0x271/0x390 fs/ext4/namei.c:2026
 ext4_add_entry+0x37b/0x8f0 fs/ext4/namei.c:2225
 ext4_add_nondir+0x31/0xa0 fs/ext4/namei.c:2553
 ext4_symlink+0x7c0/0x970 fs/ext4/namei.c:3331
 vfs_symlink fs/namei.c:4119 [inline]
 vfs_symlink+0x218/0x310 fs/namei.c:4105
 do_symlinkat+0x1a5/0x1e0 fs/namei.c:4146
 __do_sys_symlink fs/namei.c:4165 [inline]
 __se_sys_symlink fs/namei.c:4163 [inline]
 __x64_sys_symlink+0x3f/0x50 fs/namei.c:4163
 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: 16038 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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