linux-kernel - Re: [cfs_trace_lock_tcd] BUG: unable to handle kernel NULL pointer dereference at 00000050

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Date:   Wed, 18 Apr 2018 22:13:17 +0800
From:   Fengguang Wu <fengguang.wu@...el.com>
To:     James Simmons <jsimmons@...radead.org>
Cc:     Oleg Drokin <oleg.drokin@...el.com>,
        Andreas Dilger <andreas.dilger@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Denis Petrovic <denis.petrovic@....ece.fr>,
        lustre-devel@...ts.lustre.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, lkp@...org
Subject: Re: [cfs_trace_lock_tcd] BUG: unable to handle kernel NULL pointer
 dereference at 00000050

Hi James,

On Wed, Apr 18, 2018 at 02:59:15PM +0100, James Simmons wrote:
>
>> Hello,
>>
>> FYI this happens in mainline kernel 4.17.0-rc1.
>> It looks like a new regression.
>>
>> [    7.587002]  lnet_selftest_init+0x2c4/0x5d9:
>> 						lnet_selftest_init at drivers/staging/lustre/lnet/selftest/module.c:134
>> [    7.587002]  ? lnet_selftest_exit+0x8d/0x8d:
>> 						lnet_selftest_init at drivers/staging/lustre/lnet/selftest/module.c:90
>
>Are you running lnet selftest ?

Perhaps yes -- it's randconfig boot test and the .config does include
CONFIG_LNET_SELFTEST:

        CONFIG_LNET=y
        CONFIG_LNET_MAX_PAYLOAD=1048576
==>     CONFIG_LNET_SELFTEST=y
        CONFIG_LNET_XPRT_IB=y

>Is this a UMP setup?

Yes, .config has:

        # CONFIG_SMP is not set

>The reason I ask is that their is a SMP handling bug in lnet
>selftest. If you look at the mailing list I pushed a SMP patch
>series. Can you try that series and tell me if it works for you.

So it looks your fixup patch is not for this case? Anyway the
reproduce-* script attached in the previous email should be fairly
straightforward to try out for reproducing the bug.

Thanks,
Fengguang