From: Matthew Wilcox <willy@infradead.org>
To: xen@randomwebstuff.com
Cc: Laura Abbott <labbott@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, bugzilla-daemon@bugzilla.kernel.org
Subject: Re: [Bug 198497] New: handle_mm_fault / xen_pmd_val / radix_tree_lookup_slot Null pointer
Date: Fri, 19 Jan 2018 05:21:45 -0800 [thread overview]
Message-ID: <20180119132145.GB2897@bombadil.infradead.org> (raw)
In-Reply-To: <d38ff996-8294-81a6-075f-d7b2a60aa2f4@rimuhosting.com>
On Fri, Jan 19, 2018 at 04:14:42PM +1300, xen@randomwebstuff.com wrote:
>
> On 19/01/18 4:04 PM, Matthew Wilcox wrote:
> > On Thu, Jan 18, 2018 at 02:18:20PM -0800, Laura Abbott wrote:
> > > On 01/18/2018 01:55 PM, Andrew Morton wrote:
> > > > > [ 24.647744] BUG: unable to handle kernel NULL pointer dereference at
> > > > > 00000008
> > > > > [ 24.647801] IP: __radix_tree_lookup+0x14/0xa0
> > > > > [ 24.647811] *pdpt = 00000000253d6027 *pde = 0000000000000000
> > > > > [ 24.647828] Oops: 0000 [#1] SMP
> > > > > [ 24.647842] CPU: 5 PID: 3600 Comm: java Not tainted
> > > > > 4.14.13-rh10-20180115190010.xenU.i386 #1
> > > > > [ 24.647855] task: e52518c0 task.stack: e4e7a000
> > > > > [ 24.647866] EIP: __radix_tree_lookup+0x14/0xa0
> > > > > [ 24.647876] EFLAGS: 00010286 CPU: 5
> > > > > [ 24.647884] EAX: 00000004 EBX: 00000007 ECX: 00000000 EDX: 00000000
If my understanding is right, EDX contains the index we're looking up.
Which is zero. So the swp_entry we got is one bit away from being NULL.
Hmm. Have you run memtest86 or some other memory tester on the system
recently?
> PS: cannot recall seeing this issue on x86_64, just 32 bit.
Laura has 64-bit instances of this.
PPS: reminder
> this is on a Xen VM which per https://xenbits.xen.org/docs/unstable/man/xl.cfg.5.html#PVH-Guest-Specific-Options
> has "out of sync pagetables" if that is relevant (we do not set that option,
> I am unsure what default is used).
Laura also has non-Xen instances of this. They may not all be the same
bug, of course.
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next prev parent reply other threads:[~2018-01-19 13:21 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <bug-198497-27@https.bugzilla.kernel.org/>
2018-01-18 21:55 ` [Bug 198497] New: handle_mm_fault / xen_pmd_val / radix_tree_lookup_slot Null pointer Andrew Morton
2018-01-18 22:18 ` Laura Abbott
2018-01-19 3:04 ` Matthew Wilcox
2018-01-19 3:14 ` xen
2018-01-19 13:21 ` Matthew Wilcox [this message]
2018-01-19 17:30 ` Laura Abbott
2018-01-26 6:54 ` xen
2018-01-26 19:40 ` Matthew Wilcox
2018-01-29 22:26 ` xen
2018-01-31 10:54 ` Matthew Wilcox
2018-01-31 23:02 ` Tetsuo Handa
2018-02-01 9:48 ` Matthew Wilcox
2018-02-09 14:47 ` Matthew Wilcox
2018-04-12 17:12 ` Andrew Morton
2018-04-12 17:28 ` Matthew Wilcox
2018-01-19 13:33 ` Matthew Wilcox
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