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BUG: KCSAN: data-race in ext4_alloc_da_blocks / ext4_da_reserve_space

write to 0xffff8881532f8d08 of 4 bytes by task 5319 on cpu 1:
 ext4_da_reserve_space+0x147/0x200 fs/ext4/inode.c:1494
 ext4_insert_delayed_block fs/ext4/inode.c:1660 [inline]
 ext4_da_map_blocks fs/ext4/inode.c:1774 [inline]
 ext4_da_get_block_prep+0x512/0x9b0 fs/ext4/inode.c:1838
 __block_write_begin_int+0x4a2/0x1060 fs/buffer.c:2006
 __block_write_begin+0x2b/0x40 fs/buffer.c:2056
 ext4_da_write_begin+0x4a8/0x7f0 fs/ext4/inode.c:3024
 generic_perform_write+0x1a6/0x3d0 mm/filemap.c:3773
 ext4_buffered_write_iter+0x305/0x400 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11a0 fs/ext4/file.c:519
 __kernel_write+0x30c/0x5b0 fs/read_write.c:539
 kernel_write+0x160/0x2f0 fs/read_write.c:568
 p9_fd_write net/9p/trans_fd.c:430 [inline]
 p9_write_work+0x3ac/0x7c0 net/9p/trans_fd.c:481
 process_one_work+0x402/0x910 kernel/workqueue.c:2297
 worker_thread+0x636/0xae0 kernel/workqueue.c:2444
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

read to 0xffff8881532f8d08 of 4 bytes by task 23761 on cpu 0:
 ext4_alloc_da_blocks+0x1a/0xd0 fs/ext4/inode.c:3136
 ext4_release_file+0x5b/0x1d0 fs/ext4/file.c:141
 __fput+0x295/0x520 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0xae/0x130 kernel/task_work.c:164
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:175 [inline]
 exit_to_user_mode_prepare+0x156/0x190 kernel/entry/common.c:209
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x49/0x90 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000 -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 23761 Comm: syz-executor.1 Tainted: G        W         5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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