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BUG: KCSAN: data-race in fat16_ent_put / fat_parse_short

write to 0xffff8881011d0b42 of 2 bytes by task 5055 on cpu 1:
 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
 ioctl_preallocate+0x12a/0x190 fs/ioctl.c:504
 file_ioctl fs/ioctl.c:544 [inline]
 do_vfs_ioctl+0xa6b/0xd00 fs/ioctl.c:742
 ksys_ioctl+0xb2/0x150 fs/ioctl.c:761
 __do_sys_ioctl fs/ioctl.c:772 [inline]
 __se_sys_ioctl fs/ioctl.c:770 [inline]
 __x64_sys_ioctl+0x47/0x60 fs/ioctl.c:770
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881011d0b40 of 11 bytes by task 5063 on cpu 0:
 fat_parse_short+0x159/0x1140 include/linux/string.h:381
 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: 0 PID: 5063 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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