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

write to 0xffff88812aec3b98 of 8 bytes by task 11208 on cpu 1:
 ondemand_readahead+0x3aa/0x730 mm/readahead.c:470
 page_cache_sync_readahead+0x1b0/0x1e0 mm/readahead.c:527
 generic_file_buffered_read mm/filemap.c:2036 [inline]
 generic_file_read_iter+0xf24/0x18c0 mm/filemap.c:2309
 ext4_file_read_iter fs/ext4/file.c:131 [inline]
 ext4_file_read_iter+0x103/0x360 fs/ext4/file.c:114
 call_read_iter include/linux/fs.h:1901 [inline]
 generic_file_splice_read+0x2df/0x470 fs/splice.c:313
 do_splice_to+0xc7/0x100 fs/splice.c:892
 splice_direct_to_actor+0x1b9/0x540 fs/splice.c:971
 do_splice_direct+0x152/0x1d0 fs/splice.c:1080
 do_sendfile+0x380/0x800 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+0x121/0x140 fs/read_write.c:1568
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812aec3b98 of 8 bytes by task 11198 on cpu 0:
 ondemand_readahead+0xf5/0x730 mm/readahead.c:409
 page_cache_sync_readahead+0x1b0/0x1e0 mm/readahead.c:527
 generic_file_buffered_read mm/filemap.c:2036 [inline]
 generic_file_read_iter+0xf24/0x18c0 mm/filemap.c:2309
 ext4_file_read_iter fs/ext4/file.c:131 [inline]
 ext4_file_read_iter+0x103/0x360 fs/ext4/file.c:114
 call_read_iter include/linux/fs.h:1901 [inline]
 generic_file_splice_read+0x2df/0x470 fs/splice.c:313
 do_splice_to+0xc7/0x100 fs/splice.c:892
 splice_direct_to_actor+0x1b9/0x540 fs/splice.c:971
 do_splice_direct+0x152/0x1d0 fs/splice.c:1080
 do_sendfile+0x380/0x800 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+0x121/0x140 fs/read_write.c:1568
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11198 Comm: syz-executor.3 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================