KCSAN: data-race in generic_file_buffered_read / generic_file_buffered_read

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 1b504402 Merge tag 'dma-mapping-5.8-3' of git://git.infrad..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17ea864e100000
kernel config: https://syzkaller.appspot.com/x/.config?x=8d84808839c665b5
dashboard link: https://syzkaller.appspot.com/bug?extid=ab0dea0aed2dec8107a8
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)
CC: [ak...@linux-foundation.org linux-...@vger.kernel.org linu...@kvack.org]

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+ab0dea...@syzkaller.appspotmail.com

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

write to 0xffff888120abebb0 of 8 bytes by task 16062 on cpu 1:
generic_file_buffered_read+0x1624/0x1750 mm/filemap.c:2237
generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2307
ext4_file_read_iter+0x2dd/0x410 fs/ext4/file.c:73
call_read_iter include/linux/fs.h:1901 [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:1521
__do_sys_sendfile64 fs/read_write.c:1582 [inline]
__se_sys_sendfile64 fs/read_write.c:1568 [inline]
__x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1568
do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888120abebb0 of 8 bytes by task 16063 on cpu 0:
generic_file_buffered_read+0x11c/0x1750 mm/filemap.c:2011
generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2307
ext4_file_read_iter+0x2dd/0x410 fs/ext4/file.c:73
call_read_iter include/linux/fs.h:1901 [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:1521
__do_sys_sendfile64 fs/read_write.c:1582 [inline]
__se_sys_sendfile64 fs/read_write.c:1568 [inline]
__x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1568
do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 16063 Comm: syz-executor.0 Not tainted 5.8.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


---
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[Marco Elver]

#syz upstream

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