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BUG: KCSAN: data-race in fat12_ent_put / fat_parse_short

read to 0xffff888217804320 of 11 bytes by task 17708 on cpu 0:
 fat_parse_short+0x15b/0x1190 include/linux/string.h:378
 fat_search_long+0x267/0xc60 fs/fat/dir.c:507
 vfat_find+0xc1/0xd0 fs/fat/namei_vfat.c:698
 vfat_lookup+0x75/0x350 fs/fat/namei_vfat.c:712
 lookup_open fs/namei.c:3203 [inline]
 do_last fs/namei.c:3314 [inline]
 path_openat+0x15b4/0x36e0 fs/namei.c:3525
 do_filp_open+0x11e/0x1b0 fs/namei.c:3555
 do_sys_open+0x3b3/0x4f0 fs/open.c:1097
 ksys_open include/linux/syscalls.h:1385 [inline]
 __do_sys_creat fs/open.c:1155 [inline]
 __se_sys_creat fs/open.c:1153 [inline]
 __x64_sys_creat+0x45/0x60 fs/open.c:1153
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888217804322 of 1 bytes by task 17702 on cpu 1:
 fat12_ent_put+0xbe/0x1b0 fs/fat/fatent.c:164
 fat_alloc_clusters+0x507/0xc40 fs/fat/fatent.c:501
 fat_add_cluster+0x3d/0xd0 fs/fat/inode.c:107
 __fat_get_block fs/fat/inode.c:154 [inline]
 fat_get_block+0x3ae/0x4e0 fs/fat/inode.c:189
 __block_write_begin_int+0x2ea/0xf20 fs/buffer.c:1968
 __block_write_begin fs/buffer.c:2018 [inline]
 block_write_begin+0x77/0x160 fs/buffer.c:2077
 cont_write_begin+0x3d6/0x670 fs/buffer.c:2426
 fat_write_begin+0x72/0xc0 fs/fat/inode.c:235
 generic_perform_write+0x136/0x320 mm/filemap.c:3305
 __generic_file_write_iter+0x251/0x380 mm/filemap.c:3434
 generic_file_write_iter+0x28c/0x390 mm/filemap.c:3466
 call_write_iter include/linux/fs.h:1895 [inline]
 new_sync_write+0x388/0x4a0 fs/read_write.c:483
 __vfs_write+0xb1/0xc0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0xd5/0x1b0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 17702 Comm: syz-executor.4 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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