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BUG: KCSAN: data-race in ext4_itable_unused_count / ext4_itable_unused_set

read to 0xffff88821ff8805c of 2 bytes by task 21373 on cpu 0:
 ext4_itable_unused_count+0x26/0x90 fs/ext4/super.c:278
 __ext4_get_inode_loc+0x7ee/0x960 fs/ext4/inode.c:4657
 ext4_get_inode_loc+0x3f/0x50 fs/ext4/inode.c:4691
 ext4_reserve_inode_write+0x7f/0x150 fs/ext4/inode.c:5895
 ext4_mark_inode_dirty+0x7f/0x420 fs/ext4/inode.c:6047
 ext4_ext_tree_init+0x92/0xb0 fs/ext4/extents.c:860
 __ext4_new_inode+0x2c29/0x2ec0 fs/ext4/ialloc.c:1169
 ext4_symlink+0x30e/0x970 fs/ext4/namei.c:3262
 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

write to 0xffff88821ff8805c of 2 bytes by task 21376 on cpu 1:
 ext4_itable_unused_set+0x29/0x90 fs/ext4/super.c:334
 __ext4_new_inode+0x2845/0x2ec0 fs/ext4/ialloc.c:1046
 ext4_symlink+0x30e/0x970 fs/ext4/namei.c:3262
 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: 1 PID: 21376 Comm: syz-executor.3 Not tainted 5.4.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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