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BUG: KCSAN: data-race in fat16_ent_put / fat_parse_short

write to 0xffff88811cd6e58c of 2 bytes by task 16600 on cpu 1:
 fat16_ent_put+0x54/0x90 fs/fat/fatent.c:181
 fat_alloc_clusters+0x4e1/0xbf0 fs/fat/fatent.c:501
 fat_add_cluster+0x3b/0xd0 fs/fat/inode.c:108
 fat_fallocate+0x13b/0x1d0 fs/fat/file.c:291
 vfs_fallocate+0x3b1/0x640 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+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88811cd6e58c of 1 bytes by task 16604 on cpu 0:
 fat_parse_short+0x231/0x1140 fs/fat/dir.c:384
 fat_search_long+0x260/0xba0 fs/fat/dir.c:507
 vfat_find+0xb5/0xc0 fs/fat/namei_vfat.c:698
 vfat_lookup+0x73/0x340 fs/fat/namei_vfat.c:712
 lookup_open fs/namei.c:3060 [inline]
 open_last_lookups fs/namei.c:3155 [inline]
 path_openat+0xb33/0x23d0 fs/namei.c:3343
 do_filp_open+0x11e/0x1b0 fs/namei.c:3373
 do_sys_openat2+0x52e/0x680 fs/open.c:1148
 do_sys_open+0xa2/0x110 fs/open.c:1164
 ksys_open include/linux/syscalls.h:1386 [inline]
 __do_sys_creat fs/open.c:1232 [inline]
 __se_sys_creat fs/open.c:1230 [inline]
 __x64_sys_creat+0x42/0x60 fs/open.c:1230
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 16604 Comm: syz-executor.0 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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