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BUG: KCSAN: data-race in ext4_alloc_da_blocks / ext4_da_reserve_space

write to 0xffff888104bbb8b8 of 4 bytes by task 4938 on cpu 0:
 ext4_da_reserve_space+0x12b/0x220 fs/ext4/inode.c:1476
 ext4_insert_delayed_block fs/ext4/inode.c:1641 [inline]
 ext4_da_map_blocks fs/ext4/inode.c:1755 [inline]
 ext4_da_get_block_prep+0x459/0x860 fs/ext4/inode.c:1819
 ext4_block_write_begin+0x3c1/0xaa0 fs/ext4/inode.c:1061
 ext4_da_write_begin+0x4d3/0xa30 fs/ext4/inode.c:2997
 generic_perform_write+0x197/0x380 mm/filemap.c:3299
 ext4_buffered_write_iter+0x2b1/0x390 fs/ext4/file.c:270
 ext4_file_write_iter+0x4a3/0xfd0 fs/ext4/file.c:498
 call_write_iter include/linux/fs.h:1907 [inline]
 new_sync_write fs/read_write.c:484 [inline]
 __vfs_write+0x2d8/0x340 fs/read_write.c:497
 vfs_write+0x19b/0x350 fs/read_write.c:559
 ksys_write+0xce/0x180 fs/read_write.c:612
 __do_sys_write fs/read_write.c:624 [inline]
 __se_sys_write fs/read_write.c:621 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:621
 do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888104bbb8b8 of 4 bytes by task 4954 on cpu 1:
 ext4_alloc_da_blocks+0x1f/0x130 fs/ext4/inode.c:3112
 ext4_release_file+0x36/0x180 fs/ext4/file.c:142
 __fput+0x1df/0x460 fs/file_table.c:281
 ____fput+0x11/0x20 fs/file_table.c:314
 task_work_run+0x8e/0x110 kernel/task_work.c:123
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop arch/x86/entry/common.c:216 [inline]
 __prepare_exit_to_usermode+0x1c8/0x230 arch/x86/entry/common.c:246
 __syscall_return_slowpath arch/x86/entry/common.c:329 [inline]
 do_syscall_64+0xb9/0x120 arch/x86/entry/common.c:368
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 4954 Comm: syz-executor.3 Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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