KCSAN: data-race in copy_page_to_iter / fat16_ent_put (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: fc74e0a40e4f Linux 5.16-rc7
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10e3cf85b00000
kernel config: https://syzkaller.appspot.com/x/.config?x=ed0b8f6d312bd599
dashboard link: https://syzkaller.appspot.com/bug?extid=d2561ba2ea4910fc0260
compiler: Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.2
CC: [hiro...@mail.parknet.co.jp linux-...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d2561b...@syzkaller.appspotmail.com

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

write to 0xffff8881399e5216 of 2 bytes by task 21461 on cpu 0:
fat16_ent_put+0x24/0x50 fs/fat/fatent.c:182
fat_ent_write+0x5e/0xd0 fs/fat/fatent.c:416
fat_chain_add+0x15b/0x410 fs/fat/misc.c:130
fat_add_cluster fs/fat/inode.c:113 [inline]
__fat_get_block fs/fat/inode.c:155 [inline]
fat_get_block+0x48d/0x610 fs/fat/inode.c:190
__block_write_begin_int+0x4c5/0x1010 fs/buffer.c:2010
__block_write_begin fs/buffer.c:2060 [inline]
block_write_begin fs/buffer.c:2120 [inline]
cont_write_begin+0x4cf/0x7b0 fs/buffer.c:2469
fat_write_begin+0x61/0xf0 fs/fat/inode.c:235
generic_perform_write+0x1c8/0x400 mm/filemap.c:3754
__generic_file_write_iter+0x195/0x2b0 mm/filemap.c:3849
generic_file_write_iter+0x75/0x130 mm/filemap.c:3913
call_write_iter include/linux/fs.h:2162 [inline]
do_iter_readv_writev+0x2de/0x380 fs/read_write.c:725
do_iter_write+0x192/0x5c0 fs/read_write.c:851
vfs_iter_write+0x4c/0x70 fs/read_write.c:892
iter_file_splice_write+0x43a/0x790 fs/splice.c:689
do_splice_from fs/splice.c:767 [inline]
direct_splice_actor+0x80/0xa0 fs/splice.c:936
splice_direct_to_actor+0x345/0x650 fs/splice.c:891
do_splice_direct+0x106/0x190 fs/splice.c:979
do_sendfile+0x675/0xc40 fs/read_write.c:1245
__do_sys_sendfile64 fs/read_write.c:1310 [inline]
__se_sys_sendfile64 fs/read_write.c:1296 [inline]
__x64_sys_sendfile64+0x102/0x140 fs/read_write.c:1296
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 0xffff8881399e5000 of 1024 bytes by task 3031 on cpu 1:
instrument_copy_to_user include/linux/instrumented.h:119 [inline]
copyout lib/iov_iter.c:156 [inline]
copy_page_to_iter_iovec lib/iov_iter.c:228 [inline]
__copy_page_to_iter lib/iov_iter.c:852 [inline]
copy_page_to_iter+0x2cb/0x950 lib/iov_iter.c:880
filemap_read+0x138b/0x16d0 mm/filemap.c:2697
generic_file_read_iter+0x72/0x2a0 mm/filemap.c:2792
blkdev_read_iter+0x96/0x140 block/fops.c:583
call_read_iter include/linux/fs.h:2156 [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: 3031 Comm: udevd Not tainted 5.16.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.