KCSAN: data-race in mark_buffer_dirty_inode / sync_mapping_buffers (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b6505459 Linux 5.10-rc6
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14531365500000
kernel config: https://syzkaller.appspot.com/x/.config?x=c949fed53798f819
dashboard link: https://syzkaller.appspot.com/bug?extid=2ac2c251e7a08d2dc8ac
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project.git 913f6005669cfb590c99865a90bc51ed0983d09d)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

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+2ac2c2...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in mark_buffer_dirty_inode / sync_mapping_buffers

write to 0xffff88800cf562c8 of 8 bytes by task 23338 on cpu 1:
__remove_assoc_queue fs/buffer.c:481 [inline]
fsync_buffers_list fs/buffer.c:713 [inline]
sync_mapping_buffers+0x155/0x7d0 fs/buffer.c:548
fat_file_fsync+0xa9/0x100 fs/fat/file.c:194
vfs_fsync_range+0x107/0x120 fs/sync.c:200
generic_write_sync include/linux/fs.h:2739 [inline]
generic_file_write_iter+0x103/0x130 mm/filemap.c:3494
call_write_iter include/linux/fs.h:1903 [inline]
do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
do_iter_write+0x112/0x4b0 fs/read_write.c:866
vfs_iter_write+0x4c/0x70 fs/read_write.c:907
iter_file_splice_write+0x42a/0x780 fs/splice.c:686
do_splice_from fs/splice.c:764 [inline]
direct_splice_actor+0x80/0xa0 fs/splice.c:933
splice_direct_to_actor+0x345/0x650 fs/splice.c:888
do_splice_direct+0xf5/0x170 fs/splice.c:976
do_sendfile+0x5db/0xca0 fs/read_write.c:1257
__do_sys_sendfile64 fs/read_write.c:1318 [inline]
__se_sys_sendfile64 fs/read_write.c:1304 [inline]
__x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1304
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88800cf562c8 of 8 bytes by task 23329 on cpu 0:
mark_buffer_dirty_inode+0x92/0x1b0 fs/buffer.c:581
fat_mirror_bhs+0x205/0x330 fs/fat/fatent.c:396
fat_alloc_clusters+0x957/0xa50 fs/fat/fatent.c:541
fat_add_cluster fs/fat/inode.c:108 [inline]
__fat_get_block fs/fat/inode.c:155 [inline]
fat_get_block+0x213/0x5a0 fs/fat/inode.c:190
__block_write_begin_int+0x48d/0xf30 fs/buffer.c:2011
__block_write_begin fs/buffer.c:2061 [inline]
block_write_begin+0x4f/0x1b0 fs/buffer.c:2120
cont_write_begin+0x429/0x600 fs/buffer.c:2469
fat_write_begin+0x61/0xf0 fs/fat/inode.c:235
generic_perform_write+0x196/0x3a0 mm/filemap.c:3329
__generic_file_write_iter+0x15c/0x330 mm/filemap.c:3458
generic_file_write_iter+0x75/0x130 mm/filemap.c:3490
call_write_iter include/linux/fs.h:1903 [inline]
new_sync_write fs/read_write.c:518 [inline]
vfs_write+0x6d4/0x7c0 fs/read_write.c:605
ksys_write+0xce/0x180 fs/read_write.c:658
__do_sys_write fs/read_write.c:670 [inline]
__se_sys_write fs/read_write.c:667 [inline]
__x64_sys_write+0x3e/0x50 fs/read_write.c:667
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 23329 Comm: syz-executor.0 Not tainted 5.10.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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[syzbot]

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