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SubjectKCSAN: data-race in generic_file_buffered_read / generic_file_buffered_read
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Hello,

syzbot found the following issue on:

HEAD commit: e9919e11 Merge branch 'for-linus' of git://git.kernel.org/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1217a83b100000
kernel config: https://syzkaller.appspot.com/x/.config?x=570eb530a65cd98e
dashboard link: https://syzkaller.appspot.com/bug?extid=0f1e470df6a4316e0a11
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)

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+0f1e470df6a4316e0a11@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in generic_file_buffered_read / generic_file_buffered_read

write to 0xffff8880968747b0 of 8 bytes by task 6336 on cpu 0:
generic_file_buffered_read+0x18be/0x19e0 mm/filemap.c:2246
generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2326
ext4_file_read_iter+0x2d6/0x420 fs/ext4/file.c:74
call_read_iter include/linux/fs.h:1902 [inline]
generic_file_splice_read+0x22a/0x310 fs/splice.c:312
do_splice_to fs/splice.c:870 [inline]
splice_direct_to_actor+0x2a8/0x660 fs/splice.c:950
do_splice_direct+0xf2/0x170 fs/splice.c:1059
do_sendfile+0x562/0xb10 fs/read_write.c:1540
__do_sys_sendfile64 fs/read_write.c:1601 [inline]
__se_sys_sendfile64 fs/read_write.c:1587 [inline]
__x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1587
do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880968747b0 of 8 bytes by task 6334 on cpu 1:
generic_file_buffered_read+0x11e/0x19e0 mm/filemap.c:2011
generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2326
ext4_file_read_iter+0x2d6/0x420 fs/ext4/file.c:74
call_read_iter include/linux/fs.h:1902 [inline]
generic_file_splice_read+0x22a/0x310 fs/splice.c:312
do_splice_to fs/splice.c:870 [inline]
splice_direct_to_actor+0x2a8/0x660 fs/splice.c:950
do_splice_direct+0xf2/0x170 fs/splice.c:1059
do_sendfile+0x562/0xb10 fs/read_write.c:1540
__do_sys_sendfile64 fs/read_write.c:1601 [inline]
__se_sys_sendfile64 fs/read_write.c:1587 [inline]
__x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1587
do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 6334 Comm: syz-executor.0 Not tainted 5.8.0-rc5-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.
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