KCSAN: data-race in block_page_mkwrite / generic_write_end

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4ef8451b Merge tag 'perf-tools-for-v5.10-2020-11-03' of gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17a65792500000
kernel config: https://syzkaller.appspot.com/x/.config?x=76dfc991796328d4
dashboard link: https://syzkaller.appspot.com/bug?extid=ebbac9845721004d0f1a
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+ebbac9...@syzkaller.appspotmail.com

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

write to 0xffff88810d74c1d0 of 8 bytes by task 13091 on cpu 0:
i_size_write include/linux/fs.h:871 [inline]
generic_write_end+0x98/0x250 fs/buffer.c:2186
ext4_da_write_end+0x59b/0x760 fs/ext4/inode.c:3100
generic_perform_write+0x23e/0x3a0 mm/filemap.c:3322
ext4_buffered_write_iter+0x2e5/0x3d0 fs/ext4/file.c:270
ext4_file_write_iter+0x45e/0x1090 fs/ext4/file.c:503
call_write_iter include/linux/fs.h:1887 [inline]
new_sync_write fs/read_write.c:518 [inline]
vfs_write+0x617/0x690 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

read to 0xffff88810d74c1d0 of 8 bytes by task 13095 on cpu 1:
i_size_read include/linux/fs.h:849 [inline]
block_page_mkwrite+0xa9/0x2e0 fs/buffer.c:2509
ext4_page_mkwrite+0x6c6/0xe30 fs/ext4/inode.c:6082
do_page_mkwrite mm/memory.c:2703 [inline]
wp_page_shared+0x2a7/0x7c0 mm/memory.c:3032
do_wp_page+0x676/0x6c0 mm/memory.c:3125
handle_pte_fault mm/memory.c:4392 [inline]
__handle_mm_fault mm/memory.c:4509 [inline]
handle_mm_fault+0x13d1/0x1770 mm/memory.c:4607
do_user_addr_fault+0x33e/0x730 arch/x86/mm/fault.c:1372
handle_page_fault arch/x86/mm/fault.c:1429 [inline]
exc_page_fault+0x91/0x290 arch/x86/mm/fault.c:1485
asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:583
__clear_user arch/x86/lib/usercopy_64.c:24 [inline]
clear_user+0x60/0xa0 arch/x86/lib/usercopy_64.c:54
iov_iter_zero+0x14e/0xa20 lib/iov_iter.c:982
read_iter_zero+0x61/0x120 drivers/char/mem.c:718
call_read_iter include/linux/fs.h:1881 [inline]
do_iter_readv_writev+0x2e8/0x360 fs/read_write.c:738
do_iter_read+0x109/0x4b0 fs/read_write.c:801
vfs_readv fs/read_write.c:921 [inline]
do_readv+0x13d/0x280 fs/read_write.c:958
__do_sys_readv fs/read_write.c:1049 [inline]
__se_sys_readv fs/read_write.c:1046 [inline]
__x64_sys_readv+0x41/0x50 fs/read_write.c:1046
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: 13095 Comm: syz-executor.1 Not tainted 5.10.0-rc2-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.