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BUG: KCSAN: data-race in fat16_ent_put / fat_parse_short

write to 0xffff888105f00f02 of 2 bytes by task 28766 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_get_block fs/fat/inode.c:155 [inline]
 fat_get_block+0x3c6/0x4f0 fs/fat/inode.c:190
 __block_write_begin_int+0x306/0xf80 fs/buffer.c:2002
 __block_write_begin fs/buffer.c:2052 [inline]
 block_write_begin+0x76/0x160 fs/buffer.c:2111
 cont_write_begin+0x3bd/0x660 fs/buffer.c:2460
 fat_write_begin+0x69/0xc0 fs/fat/inode.c:236
 pagecache_write_begin+0x67/0x90 mm/filemap.c:3121
 cont_expand_zero fs/buffer.c:2387 [inline]
 cont_write_begin+0x176/0x660 fs/buffer.c:2450
 fat_write_begin+0x69/0xc0 fs/fat/inode.c:236
 pagecache_write_begin+0x67/0x90 mm/filemap.c:3121
 generic_cont_expand_simple+0xae/0x120 fs/buffer.c:2351
 fat_cont_expand+0x44/0x190 fs/fat/file.c:222
 fat_fallocate+0x195/0x1d0 fs/fat/file.c:300
 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 0xffff888105f00f00 of 11 bytes by task 28788 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: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_open fs/open.c:1170 [inline]
 __se_sys_open fs/open.c:1168 [inline]
 __x64_sys_open+0x50/0x60 fs/open.c:1168
 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: 28788 Comm: syz-executor.4 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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