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BUG: KCSAN: data-race in blk_mq_get_request / blk_mq_get_request

read to 0xffff888129a63148 of 8 bytes by task 22620 on cpu 0:
 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
 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

write to 0xffff888129a63148 of 8 bytes by task 22621 on cpu 1:
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 22621 Comm: syz-executor.2 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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