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

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Message-ID: <5b3d6ad6-a506-7dae-0eb7-b7da080f6454@molgen.mpg.de>
Date:   Tue, 15 Feb 2022 10:16:41 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>,
        LKML <linux-kernel@...r.kernel.org>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Jann Horn <jannh@...gle.com>
Subject: Re: BUG: KCSAN: data-race in add_device_randomness+0x20d/0x290

Dear Jason,


Thank you for your quick response, and sorry for the late reply.

Am 07.02.22 um 19:42 schrieb Jason A. Donenfeld:

> Thanks for the report. I assume that this is actually an old bug. Do
> you have a vmlinux or a random.o from this kernel you could send me to
> double check?

I had unfortunately already overwritten these files. I was unable to 
fully reproduce the same trace with a build from the same commit, and 
only got:

```
[…]
[   12.819273] BUG: KCSAN: data-race in _mix_pool_bytes+0x5d/0x1c0

[   12.822917] race at unknown origin, with read to 0xffffa21c07003009 
of 1 bytes by task 1035 on cpu 0:
[   12.823580]  _mix_pool_bytes+0x5d/0x1c0
[   12.823678]  add_device_randomness+0x97/0x290
[   12.823691]  release_task+0x231/0xb20
[   12.823735]  wait_consider_task+0x883/0x17d0
[   12.823755]  do_wait+0x35f/0x4d0
[   12.823768]  kernel_wait4+0xdb/0x180
[   12.823778]  __do_sys_wait4+0x85/0x90
[   12.823787]  __x64_sys_wait4+0x49/0x50
[   12.823797]  do_syscall_64+0x39/0x80
[   12.823819]  entry_SYSCALL_64_after_hwframe+0x44/0xae

[   12.824028] value changed: 0x56 -> 0xc1

[   12.824415] Reported by Kernel Concurrency Sanitizer on:
[   12.824688] CPU: 0 PID: 1035 Comm: postfix-script Not tainted 
5.17.0-rc2-00352-g90c9e950c0de #40
[   12.824705] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), 
BIOS 1.15.0-1 04/01/2014
[…]
```

So instead of the former (used as subject line)

     add_device_randomness+0x20d/0x290

there is

     add_device_randomness+0x97/0x290

I uploaded `random.o` [1].


Kind regards,

Paul


[1]: https://owww.molgen.mpg.de/~pmenzel/random.o