linux-kernel - Re: perf: perf_fuzzer quickly locks up on 4.15-rc7

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Date:   Thu, 11 Jan 2018 18:03:47 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vince Weaver <vincent.weaver@...ne.edu>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: perf: perf_fuzzer quickly locks up on 4.15-rc7

On Thu, Jan 11, 2018 at 11:58:24AM -0500, Vince Weaver wrote:
> On Thu, 11 Jan 2018, Vince Weaver wrote:
> 
> > On Thu, 11 Jan 2018, Peter Zijlstra wrote:
> > 
> > > OK, I'm going to try fuzzing as a user with paranoid=0, and if that
> > > doesn't help, I'm going to switch to linus' tree with my patches on.
> > 
> > OK, I'm fuzzing on a core2 machine and it locks up too.
> > 
> > It did give the following first (but it kept going for at least a minute 
> > after this oops before locking solid).
> 
> This was missing the first few lines which made it to the serial log but 
> not the console:
> 
> [  823.919729] BUG: unable to handle kernel paging request at ffff88011a7a1000
> [  823.926928] IP: 0x7fbda0042b3c
> 
> I'm dumping vmlinux and can't find address 0x7fbda0042b3c at all.

That's a user address..

> Should I be able to find it there?  Or is KASLR/KPTI or similar stopping 
> me?

Something is definitely funny, lemme try and make sense of this splat.

> > Jan 11 11:38:57 core2 kernel: [  823.930123] PGD 22ea067 P4D 22ea067 PUD 22ed067 PMD 11a520063 PTE 800000011a7a1063
> > Jan 11 11:38:57 core2 kernel: [  823.938012] Oops: 0002 [#1] SMP PTI
> > Jan 11 11:38:57 core2 kernel: [  823.968898] CPU: 1 PID: 17688 Comm: perf_fuzzer Not tainted 4.15.0-rc7+ #211
> > Jan 11 11:38:57 core2 kernel: [  823.976152] Hardware name: AOpen   DE7000/nMCP7ALPx-DE R1.06 Oct.19.2012, BIOS 080015  10/19/2012
> > Jan 11 11:38:57 core2 kernel: [  823.985259] RIP: 0033:0x7fbda0042b3c
> > Jan 11 11:38:57 core2 kernel: [  823.989002] RSP: 002b:00007ffed7fa46c8 EFLAGS: 00010246
> > Jan 11 11:38:57 core2 kernel: [  823.994434] RAX: 000000000000462d RBX: 000000000000000c RCX: 00007fbda0042b3c
> > Jan 11 11:38:57 core2 kernel: [  824.001786] RDX: 0000000000000000 RSI: 00007ffed7fa46dc RDI: 000000000000462d
> > Jan 11 11:38:57 core2 kernel: [  824.009135] RBP: 00007ffed7fa46e0 R08: 00007fbda032e0e4 R09: 0000000000000000
> > Jan 11 11:38:57 core2 kernel: [  824.016483] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401950
> > Jan 11 11:38:57 core2 kernel: [  824.023832] R13: 00007ffed7fa6ae0 R14: 0000000000000000 R15: 0000000000000000
> > Jan 11 11:38:57 core2 kernel: [  824.031198] FS:  00007fbda0540700(0000) GS:ffff88011fc80000(0000) knlGS:0000000000000000
> > Jan 11 11:38:57 core2 kernel: [  824.039530] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > Jan 11 11:38:57 core2 kernel: [  824.045477] CR2: ffff88011a7a1000 CR3: 000000011a998000 CR4: 00000000000407e0
> > Jan 11 11:38:57 core2 kernel: [  824.052827] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > Jan 11 11:38:57 core2 kernel: [  824.060176] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
> > Jan 11 11:38:57 core2 kernel: [  824.072767] CR2: ffff88011a7a1000
> > Jan 11 11:38:57 core2 kernel: [  824.076248] ---[ end trace 31d5336f74638197 ]--
> > 
>