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BUG: KCSAN: data-race in fat12_ent_put / fat_parse_short

write to 0xffff8881164dc50c of 1 bytes by task 1493 on cpu 0:
 fat12_ent_put+0x137/0x1b0 fs/fat/fatent.c:166
 fat_free_clusters+0x26a/0x690 fs/fat/fatent.c:595
 fat_free fs/fat/file.c:375 [inline]
 fat_truncate_blocks+0x4bf/0x6f0 fs/fat/file.c:393
 fat_setattr+0x7d9/0x810 fs/fat/file.c:537
 notify_change+0x82b/0xb00 fs/attr.c:336
 do_truncate+0xf9/0x180 fs/open.c:64
 handle_truncate fs/namei.c:3083 [inline]
 do_last fs/namei.c:3496 [inline]
 path_openat+0x1241/0x2f70 fs/namei.c:3607
 do_filp_open+0x11e/0x1b0 fs/namei.c:3637
 do_sys_openat2+0x4f5/0x620 fs/open.c:1149
 do_sys_open+0xa2/0x110 fs/open.c:1165
 ksys_open include/linux/syscalls.h:1386 [inline]
 __do_sys_creat fs/open.c:1233 [inline]
 __se_sys_creat fs/open.c:1231 [inline]
 __x64_sys_creat+0x42/0x60 fs/open.c:1231
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881164dc50c of 1 bytes by task 1490 on cpu 1:
 fat_parse_short+0x6f9/0x1140 fs/fat/dir.c:420
 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:3288 [inline]
 do_last fs/namei.c:3401 [inline]
 path_openat+0x15ce/0x2f70 fs/namei.c:3607
 do_filp_open+0x11e/0x1b0 fs/namei.c:3637
 do_sys_openat2+0x4f5/0x620 fs/open.c:1149
 do_sys_open+0xa2/0x110 fs/open.c:1165
 ksys_open include/linux/syscalls.h:1386 [inline]
 __do_sys_open fs/open.c:1171 [inline]
 __se_sys_open fs/open.c:1169 [inline]
 __x64_sys_open+0x50/0x60 fs/open.c:1169
 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: 1490 Comm: syz-executor.4 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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