KCSAN: data-race in generic_file_read_iter / ondemand

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BUG: KCSAN: data-race in generic_file_read_iter / ondemand_readahead

write to 0xffff88812ac0b0b0 of 8 bytes by task 28062 on cpu 0:
 generic_file_buffered_read mm/filemap.c:2240 [inline]
 generic_file_read_iter+0xb0f/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 0xffff88812ac0b0b0 of 8 bytes by task 28056 on cpu 1:
 ondemand_readahead+0x1a8/0x730 mm/readahead.c:452
 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: 1 PID: 28056 Comm: syz-executor.1 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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Time	Kernel	Commit	Syzkaller	Config	Log	Report	Manager
2020/05/25 09:11	https://github.com/google/ktsan.git kcsan	7c3cd68e5d38	11284182	.config	console log	report	ci2-upstream-kcsan-gce
2020/04/17 22:49	https://github.com/google/ktsan.git kcsan	7c3cd68e5d38	435c6d53	.config	console log	report	ci2-upstream-kcsan-gce
2020/04/08 16:33	https://github.com/google/ktsan.git kcsan	40959e34d670	db9bcd4b	.config	console log	report	ci2-upstream-kcsan-gce
2020/03/19 10:22	https://github.com/google/ktsan.git kcsan	40959e34d670	2c31c529	.config	console log	report	ci2-upstream-kcsan-gce
2020/03/03 13:30	https://github.com/google/ktsan.git kcsan	766d004d1b85	350a7a26	.config	console log	report	ci2-upstream-kcsan-gce
2020/02/25 04:02	https://github.com/google/ktsan.git kcsan	766d004d1b85	59b57593	.config	console log	report	ci2-upstream-kcsan-gce
2019/12/19 01:42	https://github.com/google/ktsan.git kcsan	245a43005292	79b211f7	.config	console log	report	ci2-upstream-kcsan-gce