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BUG: KCSAN: data-race in fat16_ent_put / fat_get_short_entry

write to 0xffff88810900c2ca of 2 bytes by task 8029 on cpu 0:
 fat16_ent_put+0x54/0x90 fs/fat/fatent.c:181
 fat_ent_write+0x69/0xf0 fs/fat/fatent.c:415
 fat_chain_add+0x356/0x410 fs/fat/misc.c:130
 fat_add_cluster+0x91/0xd0 fs/fat/inode.c:113
 fat_fallocate+0x13b/0x1d0 fs/fat/file.c:291
 vfs_fallocate+0x3b1/0x650 fs/open.c:309
 ksys_fallocate+0x5b/0xa0 fs/open.c:332
 __do_sys_fallocate fs/open.c:340 [inline]
 __se_sys_fallocate fs/open.c:338 [inline]
 __x64_sys_fallocate+0x59/0x70 fs/open.c:338
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810900c2cb of 1 bytes by task 8050 on cpu 1:
 fat_get_short_entry+0x146/0x1d0 fs/fat/dir.c:879
 fat_scan+0xb7/0x190 fs/fat/dir.c:962
 vfat_find_form+0x3a/0xb0 fs/fat/namei_vfat.c:239
 vfat_create_shortname fs/fat/namei_vfat.c:448 [inline]
 vfat_build_slots fs/fat/namei_vfat.c:611 [inline]
 vfat_add_entry+0x18f9/0x1b50 fs/fat/namei_vfat.c:672
 vfat_mkdir+0xbb/0x310 fs/fat/namei_vfat.c:865
 vfs_mkdir+0x281/0x390 fs/namei.c:3889
 do_mkdirat+0x1b5/0x200 fs/namei.c:3912
 __do_sys_mkdir fs/namei.c:3928 [inline]
 __se_sys_mkdir fs/namei.c:3926 [inline]
 __x64_sys_mkdir+0x3d/0x50 fs/namei.c:3926
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8050 Comm: syz-executor.5 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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