==================================================================
BUG: KCSAN: data-race in copy_page_to_iter / fat16_ent_put

write to 0xffff88814a585252 of 2 bytes by task 7834 on cpu 0:
 fat16_ent_put+0x24/0x50 fs/fat/fatent.c:182
 fat_alloc_clusters+0x493/0xab0 fs/fat/fatent.c:502
 fat_add_cluster fs/fat/inode.c:108 [inline]
 __fat_get_block fs/fat/inode.c:155 [inline]
 fat_get_block+0x267/0x610 fs/fat/inode.c:190
 __block_write_begin_int+0x47c/0xf90 fs/buffer.c:2010
 __block_write_begin fs/buffer.c:2060 [inline]
 block_write_begin fs/buffer.c:2121 [inline]
 cont_write_begin+0x4fb/0x7e0 fs/buffer.c:2470
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:235
 pagecache_write_begin+0x5a/0x70 mm/filemap.c:3532
 cont_expand_zero fs/buffer.c:2397 [inline]
 cont_write_begin+0x172/0x7e0 fs/buffer.c:2460
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:235
 pagecache_write_begin+0x5a/0x70 mm/filemap.c:3532
 generic_cont_expand_simple+0x93/0x120 fs/buffer.c:2361
 fat_cont_expand+0x3a/0x160 fs/fat/file.c:222
 fat_setattr+0x391/0x940 fs/fat/file.c:503
 notify_change+0x924/0xbf0 fs/attr.c:410
 do_truncate fs/open.c:65 [inline]
 do_sys_ftruncate+0x323/0x430 fs/open.c:193
 __do_sys_ftruncate fs/open.c:204 [inline]
 __se_sys_ftruncate fs/open.c:202 [inline]
 __x64_sys_ftruncate+0x2f/0x40 fs/open.c:202
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88814a585000 of 1024 bytes by task 7833 on cpu 1:
 instrument_copy_to_user include/linux/instrumented.h:119 [inline]
 copyout lib/iov_iter.c:154 [inline]
 copy_page_to_iter_iovec lib/iov_iter.c:226 [inline]
 __copy_page_to_iter lib/iov_iter.c:850 [inline]
 copy_page_to_iter+0x2cb/0x950 lib/iov_iter.c:878
 copy_folio_to_iter include/linux/uio.h:153 [inline]
 filemap_read+0x1126/0x1430 mm/filemap.c:2649
 blkdev_read_iter+0xcb/0x350 block/fops.c:610
 call_read_iter include/linux/fs.h:2080 [inline]
 new_sync_read fs/read_write.c:400 [inline]
 vfs_read+0x66c/0x750 fs/read_write.c:481
 ksys_read+0xd9/0x190 fs/read_write.c:619
 __do_sys_read fs/read_write.c:629 [inline]
 __se_sys_read fs/read_write.c:627 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:627
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7833 Comm: udevd Not tainted 5.16.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================
I/O error, dev loop5, sector 16128 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
I/O error, dev loop4, sector 16128 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0