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Subject: Re: [PATCH] VM, x86, PAT: Change implementation of
 is_linear_pfn_mapping
From: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
To: Frans Pop <elendil@planet.nl>
Cc: "mingo@elte.hu" <mingo@elte.hu>,
       "thellstrom@vmware.com" <thellstrom@vmware.com>,
       Linux kernel mailing list <linux-kernel@vger.kernel.org>,
       "Siddha, Suresh B" <suresh.b.siddha@intel.com>,
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Date: Wed, 11 Mar 2009 17:31:52 -0700
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On Wed, 2009-03-11 at 15:09 -0700, Frans Pop wrote:
> Pallipadi, Venkatesh wrote:
> > Use of vma->vm_pgoff to identify the pfnmaps that are fully
> > mapped at mmap time is broke. vm_pgoff is set by generic mmap
> > code even for cases where drivers are setting up the mappings
> > at the fault time.
> > 
> > The problem was originally reported here.
> > http://marc.info/?l=linux-kernel&m=123383810628583&w=2
> > 
> > Change is_linear_pfn_mapping logic to overload VM_NONLINEAR
> > flag along with VM_PFNMAP to mean full PFNMAP setup at mmap
> > time.
> > 
> > Acked-by: Thomas Hellstrom <thellstrom@vmware.com>
> > Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
> > Signed-off-by: Suresh Siddha <suresh.b.siddha>@intel.com>
> 
> I've applied this patch on top of v2.6.29-rc7-143-g99adcd9 [1] and since 
> then I've had my system, or rather X/KDE, hang several times. The last 
> time the problem seems to have been KDE's kicker. I was running a kernel 
> compile in a konsole window and that just continued and finished, but the 
> keyboard was completely dead.
> I could still ssh in from another box. 'ps' would show the top processes, 
> but hang as well at some point (in the middle of listing KDE processes.
> 
> The hang was with pat enabled. I've now booted with nopat.

Frans,

Thanks for testing this. I don't seem to reproduce this on any of my
test systems with this patch on either tip or latest git. Do you see the
hang on every boot or once in a while? Are things stable with nopat?

> The log shows (full log attached):
> kernel: BUG: unable to handle kernel NULL pointer dereference at
> 0000000000000008
> kernel: IP: [<ffffffff80322504>] prio_tree_remove+0x9c/0xcc
> kernel: PGD 7cab1067 PUD 7d644067 PMD 0
> kernel: Oops: 0000 [#1] SMP
> kernel: last sysfs file: /sys/class/power_supply/C23D/charge_full
> kernel: CPU 1
> kernel: Pid: 5415, comm: kicker Not tainted 2.6.29-rc7 #4 HP Comp
> aq 2510p Notebook PC
> kernel: RIP: 0010:[<ffffffff80322504>]  [<ffffffff80322504>] prio
> _tree_remove+0x9c/0xcc
> [...]
> kernel: Call Trace:
> kernel:  [<ffffffff803225df>] prio_tree_insert+0xab/0x22a
> kernel:  [<ffffffff8027e90d>] vma_prio_tree_insert+0x23/0xc2
> kernel:  [<ffffffff802864af>] __vma_link_file+0x70/0x72
> kernel:  [<ffffffff80286c15>] vma_link+0x7d/0xab
> kernel:  [<ffffffff802881ea>] mmap_region+0x313/0x479
> kernel:  [<ffffffff80288646>] do_mmap_pgoff+0x2f6/0x35c
> kernel:  [<ffffffff802ea99a>] do_shmat+0x28a/0x36c
> kernel:  [<ffffffff802eaa8d>] sys_shmat+0x11/0x1c
> kernel:  [<ffffffff8020c25b>] system_call_fastpath+0x16/0x1b
> 
> From the symptoms I strongly suspect this patch to be the culprit.
> 
> [1] Together with some other patches (mainly Rafael's latest patchset 
> for "Rework disabling of interrupts during suspend-resume"), but I doubt 
> any of those are related to this issue.
> 

Nothing obvious strikes me with this patch and above OOPs. Can you
please try this patch alone on latest git and check whether you still
see the failures?

Thanks,
Venki

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