linux-kernel - BUG: KCSAN: data-race in add_device

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Message-ID: <e10b79cf-d6d5-ffcc-bce4-edd92b7cb6b9@molgen.mpg.de>
Date:   Mon, 7 Feb 2022 17:14:18 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     "Theodore Y. Ts'o" <tytso@....edu>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: BUG: KCSAN: data-race in add_device_randomness+0x20d/0x290

Dear Linux folks,


Running Linux 5.17-rc2+ in QEMU 6.2.0 the Kernel Concurrency Sanitizer 
reports the race below:

     qemu-system-x86_64 -cpu host -smp cpus=3 -m 2G -enable-kvm -usb 
-device usb-host,vendorid=0x8087,productid=0x0a2a -drive 
file=/dev/shm/debian-64.img,format=raw,if=virtio -net nic -net 
user,hostfwd=tcp::22223-:22 -kernel /dev/shm/bzImage -append 
"root=/dev/vda1 rw quiet"

```
[    3.383861] 
==================================================================
[    3.385662] BUG: KCSAN: data-race in add_device_randomness+0x20d/0x290
[    3.387142]
[    3.387905] race at unknown origin, with read to 0xffff9ec881ad3008 
of 1 bytes by task 44 on cpu 0:
[    3.389778]  add_device_randomness+0x20d/0x290
[    3.389789]  release_task+0x231/0xb20
[    3.389800]  wait_consider_task+0x883/0x17d0
[    3.389809]  do_wait+0x2b4/0x4d0
[    3.389818]  kernel_wait+0x71/0xd0
[    3.389827]  call_usermodehelper_exec_work+0xa3/0xb0
[    3.389838]  process_one_work+0x477/0x7d0
[    3.389845]  worker_thread+0x2ec/0x810
[    3.389851]  kthread+0x16d/0x1a0
[    3.389860]  ret_from_fork+0x22/0x30
[    3.389868]
[    3.390623] value changed: 0x00 -> 0x43
[    3.391594]
[    3.392363] Reported by Kernel Concurrency Sanitizer on:
[    3.394131] CPU: 0 PID: 44 Comm: kworker/u6:2 Not tainted 
5.17.0-rc2-00353-g90c9e950c0de #34
[    3.394151] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), 
BIOS 1.15.0-1 04/01/2014
[    3.394190] Workqueue: events_unbound call_usermodehelper_exec_work
```

Please find the output of `dmesg` attached.


Kind regards,

Paul
View attachment "linux-5.17-rc2-kcsan-add_device_randomness.txt" of type "text/plain" (29356 bytes)