KCSAN: data-race in generic_file_read_iter / simple_write_end

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: b12d66a6 mm, kcsan: Instrument SLAB free with ASSERT_EXCLU..
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=1070a47ee00000
kernel config: https://syzkaller.appspot.com/x/.config?x=10bc0131c4924ba9
dashboard link: https://syzkaller.appspot.com/bug?extid=b73aa457fa6c704f0d60
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk el...@google.com]

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b73aa4...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in generic_file_read_iter / simple_write_end

write to 0xffff888128fabd08 of 8 bytes by task 18272 on cpu 1:
i_size_write include/linux/fs.h:888 [inline]
simple_write_end+0x1d0/0x370 fs/libfs.c:587
generic_perform_write+0x1d3/0x320 mm/filemap.c:3298
__generic_file_write_iter+0x251/0x380 mm/filemap.c:3416
generic_file_write_iter+0x28c/0x38c mm/filemap.c:3448
call_write_iter include/linux/fs.h:1901 [inline]
do_iter_readv_writev+0x487/0x5b0 fs/read_write.c:693
do_iter_write fs/read_write.c:998 [inline]
do_iter_write+0x13b/0x3c0 fs/read_write.c:979
vfs_iter_write+0x5c/0x80 fs/read_write.c:1039
iter_file_splice_write+0x536/0x850 fs/splice.c:760
do_splice_from fs/splice.c:863 [inline]
direct_splice_actor+0xa0/0xc0 fs/splice.c:1037
splice_direct_to_actor+0x22b/0x540 fs/splice.c:992
do_splice_direct+0x161/0x1e0 fs/splice.c:1080
do_sendfile+0x384/0x7f0 fs/read_write.c:1520
__do_sys_sendfile64 fs/read_write.c:1575 [inline]
__se_sys_sendfile64 fs/read_write.c:1567 [inline]
__x64_sys_sendfile64+0xbe/0x140 fs/read_write.c:1567
do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888128fabd08 of 8 bytes by task 18308 on cpu 0:
generic_file_buffered_read mm/filemap.c:2084 [inline]
generic_file_read_iter+0x860/0x1440 mm/filemap.c:2302
call_read_iter include/linux/fs.h:1895 [inline]
generic_file_splice_read+0x35c/0x500 fs/splice.c:313
do_splice_to+0xf2/0x130 fs/splice.c:892
splice_direct_to_actor+0x1b6/0x540 fs/splice.c:971
do_splice_direct+0x161/0x1e0 fs/splice.c:1080
do_sendfile+0x384/0x7f0 fs/read_write.c:1520
__do_sys_sendfile64 fs/read_write.c:1575 [inline]
__se_sys_sendfile64 fs/read_write.c:1567 [inline]
__x64_sys_sendfile64+0xbe/0x140 fs/read_write.c:1567
do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 18308 Comm: syz-executor.5 Not tainted 5.6.0-rc1-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.