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

write to 0xffff88811c4ca2e8 of 2 bytes by task 6745 on cpu 0:
 fat16_ent_put+0x24/0x50 fs/fat/fatent.c:182
 fat_alloc_clusters+0x47d/0xa80 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+0x263/0x600 fs/fat/inode.c:190
 __block_write_begin_int+0x33d/0xc90 fs/buffer.c:2006
 __block_write_begin fs/buffer.c:2056 [inline]
 block_write_begin+0x77/0x170 fs/buffer.c:2117
 cont_write_begin+0x3cf/0x500 fs/buffer.c:2463
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:235
 pagecache_write_begin+0x5a/0x70 mm/filemap.c:3631
 cont_expand_zero fs/buffer.c:2390 [inline]
 cont_write_begin+0x17e/0x500 fs/buffer.c:2453
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:235
 pagecache_write_begin+0x5a/0x70 mm/filemap.c:3631
 generic_cont_expand_simple+0x90/0x120 fs/buffer.c:2355
 fat_cont_expand+0x3a/0x160 fs/fat/file.c:223
 fat_setattr+0x34a/0x880 fs/fat/file.c:504
 notify_change+0x9c3/0xa30 fs/attr.c:410
 do_truncate fs/open.c:65 [inline]
 do_sys_ftruncate+0x317/0x420 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+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88811c4ca000 of 1377 bytes by task 2145 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:852 [inline]
 copy_page_to_iter+0x415/0x7b0 lib/iov_iter.c:880
 copy_folio_to_iter include/linux/uio.h:153 [inline]
 filemap_read+0x10b2/0x1400 mm/filemap.c:2730
 blkdev_read_iter+0x2c6/0x370 block/fops.c:611
 call_read_iter include/linux/fs.h:2044 [inline]
 new_sync_read fs/read_write.c:401 [inline]
 vfs_read+0x5a5/0x6a0 fs/read_write.c:482
 ksys_read+0xe8/0x1a0 fs/read_write.c:620
 __do_sys_read fs/read_write.c:630 [inline]
 __se_sys_read fs/read_write.c:628 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:628
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 2145 Comm: udevd Not tainted 5.18.0-rc5-syzkaller-00006-g9050ba3a61a4-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================