KCSAN: data-race in mm_update_next_owner / page_cache_ra_unbounded

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e87297fa Merge tag 'drm-fixes-2020-12-04' of git://anongit..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14c24dbb500000
kernel config: https://syzkaller.appspot.com/x/.config?x=c949fed53798f819
dashboard link: https://syzkaller.appspot.com/bug?extid=60f8baa47292518d18d8
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project.git 913f6005669cfb590c99865a90bc51ed0983d09d)
CC: [ak...@linux-foundation.org linux-...@vger.kernel.org linu...@kvack.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+60f8ba...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in mm_update_next_owner / page_cache_ra_unbounded

write to 0xffff88812d342064 of 4 bytes by task 31805 on cpu 0:
memalloc_nofs_save include/linux/sched/mm.h:228 [inline]
page_cache_ra_unbounded+0xae/0x4c0 mm/readahead.c:193
do_page_cache_ra mm/readahead.c:267 [inline]
force_page_cache_ra+0x226/0x260 mm/readahead.c:298
page_cache_sync_ra+0x194/0x1c0 mm/readahead.c:572
page_cache_sync_readahead include/linux/pagemap.h:839 [inline]
generic_file_buffered_read+0x388/0x23a0 mm/filemap.c:2235
generic_file_read_iter+0x80/0x3d0 mm/filemap.c:2553
blkdev_read_iter+0xb3/0xc0 fs/block_dev.c:1925
call_read_iter include/linux/fs.h:1897 [inline]
new_sync_read fs/read_write.c:415 [inline]
vfs_read+0x552/0x5c0 fs/read_write.c:496
ksys_read+0xce/0x180 fs/read_write.c:634
__do_sys_read fs/read_write.c:644 [inline]
__se_sys_read fs/read_write.c:642 [inline]
__x64_sys_read+0x3e/0x50 fs/read_write.c:642
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812d342064 of 4 bytes by task 3353 on cpu 1:
mm_update_next_owner+0x1d9/0x4e0 kernel/exit.c:387
exit_mm+0x2ff/0x370 kernel/exit.c:485
do_exit+0x3c8/0x1630 kernel/exit.c:796
do_group_exit+0x16f/0x170 kernel/exit.c:906
__do_sys_exit_group+0xb/0x10 kernel/exit.c:917
__se_sys_exit_group+0x5/0x10 kernel/exit.c:915
__x64_sys_exit_group+0x16/0x20 kernel/exit.c:915
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: 1 PID: 3353 Comm: syz-executor.4 Not tainted 5.10.0-rc6-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.