[moderation] [exfat?] KCSAN: data-race in fat_bmap / generic_write_end (7)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b401b621758e Linux 6.8-rc5
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12cca09c180000
kernel config: https://syzkaller.appspot.com/x/.config?x=7507056e4ee79a
dashboard link: https://syzkaller.appspot.com/bug?extid=2f4e90a084ee920bddfe
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
CC: [hiro...@mail.parknet.co.jp linki...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org sj155...@samsung.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/292988b16d14/disk-b401b621.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/87ac90addfde/vmlinux-b401b621.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f1b26db595a7/bzImage-b401b621.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2f4e90...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in fat_bmap / generic_write_end

write to 0xffff888106a4d318 of 8 bytes by task 27954 on cpu 1:
i_size_write include/linux/fs.h:932 [inline]
generic_write_end+0x94/0x230 fs/buffer.c:2275
fat_write_end+0x4e/0x160 fs/fat/inode.c:244
generic_perform_write+0x267/0x410 mm/filemap.c:3941
__generic_file_write_iter+0xec/0x120 mm/filemap.c:4022
generic_file_write_iter+0x7d/0x1c0 mm/filemap.c:4051
call_write_iter include/linux/fs.h:2085 [inline]
iter_file_splice_write+0x5de/0x950 fs/splice.c:743
do_splice_from fs/splice.c:941 [inline]
direct_splice_actor+0x167/0x2c0 fs/splice.c:1164
splice_direct_to_actor+0x2fb/0x660 fs/splice.c:1108
do_splice_direct_actor fs/splice.c:1207 [inline]
do_splice_direct+0xd7/0x150 fs/splice.c:1233
do_sendfile+0x3b9/0x960 fs/read_write.c:1295
__do_sys_sendfile64 fs/read_write.c:1362 [inline]
__se_sys_sendfile64 fs/read_write.c:1348 [inline]
__x64_sys_sendfile64+0x110/0x150 fs/read_write.c:1348
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff888106a4d318 of 8 bytes by task 27980 on cpu 0:
i_size_read include/linux/fs.h:910 [inline]
is_exceed_eof fs/fat/cache.c:340 [inline]
fat_bmap+0x1d2/0x290 fs/fat/cache.c:375
__fat_get_block fs/fat/inode.c:129 [inline]
fat_get_block+0xd1/0x5e0 fs/fat/inode.c:190
do_mpage_readpage+0x47b/0xca0 fs/mpage.c:232
mpage_readahead+0x1ad/0x2d0 fs/mpage.c:381
fat_readahead+0x1c/0x20 fs/fat/inode.c:210
read_pages+0x9f/0x540 mm/readahead.c:160
page_cache_ra_unbounded+0x224/0x2e0
do_page_cache_ra mm/readahead.c:299 [inline]
page_cache_ra_order mm/readahead.c:544 [inline]
ondemand_readahead+0x50b/0x670 mm/readahead.c:666
page_cache_sync_ra+0x27e/0x2a0 mm/readahead.c:693
page_cache_sync_readahead include/linux/pagemap.h:1300 [inline]
filemap_get_pages+0x251/0xf90 mm/filemap.c:2498
filemap_splice_read+0x337/0x8f0 mm/filemap.c:2872
do_splice_read fs/splice.c:985 [inline]
splice_direct_to_actor+0x268/0x660 fs/splice.c:1089
do_splice_direct_actor fs/splice.c:1207 [inline]
do_splice_direct+0xd7/0x150 fs/splice.c:1233
do_sendfile+0x3b9/0x960 fs/read_write.c:1295
__do_sys_sendfile64 fs/read_write.c:1362 [inline]
__se_sys_sendfile64 fs/read_write.c:1348 [inline]
__x64_sys_sendfile64+0x110/0x150 fs/read_write.c:1348
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x000000000019d000 -> 0x000000000019e000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 27980 Comm: syz-executor.3 Not tainted 6.8.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
==================================================================


---
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.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[syzbot]

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