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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 8642 on cpu 0:
 ext4_itable_unused_count+0x26/0x90 fs/ext4/super.c:278
 __ext4_get_inode_loc+0x7ee/0x960 fs/ext4/inode.c:4321
 ext4_get_inode_loc+0x3f/0x50 fs/ext4/inode.c:4355
 ext4_reserve_inode_write+0x7f/0x150 fs/ext4/inode.c:5566
 ext4_mark_inode_dirty+0x7f/0x420 fs/ext4/inode.c:5732
 ext4_ext_tree_init+0x92/0xb0 fs/ext4/extents.c:872
 __ext4_new_inode+0x2d94/0x2f10 fs/ext4/ialloc.c:1164
 ext4_symlink+0x31c/0x9b0 fs/ext4/namei.c:3275
 vfs_symlink fs/namei.c:4131 [inline]
 vfs_symlink+0x218/0x310 fs/namei.c:4117
 do_symlinkat+0x1a5/0x1e0 fs/namei.c:4158
 __do_sys_symlink fs/namei.c:4177 [inline]
 __se_sys_symlink fs/namei.c:4175 [inline]
 __x64_sys_symlink+0x3f/0x50 fs/namei.c:4175
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88821ff8805c of 2 bytes by task 8639 on cpu 1:
 ext4_itable_unused_set+0x29/0x90 fs/ext4/super.c:334
 __ext4_new_inode+0x2894/0x2f10 fs/ext4/ialloc.c:1041
 ext4_symlink+0x31c/0x9b0 fs/ext4/namei.c:3275
 vfs_symlink fs/namei.c:4131 [inline]
 vfs_symlink+0x218/0x310 fs/namei.c:4117
 do_symlinkat+0x1a5/0x1e0 fs/namei.c:4158
 __do_sys_symlink fs/namei.c:4177 [inline]
 __se_sys_symlink fs/namei.c:4175 [inline]
 __x64_sys_symlink+0x3f/0x50 fs/namei.c:4175
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8639 Comm: syz-executor.2 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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