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Date: Sat, 11 Apr 2015 12:57:13 -0500
From: Alan Cox <alc@rice.edu>
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To: Svatopluk Kraus <onwahe@gmail.com>, freebsd-current@freebsd.org,
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Subject: Re: [patch] deadlock in vm_reserv_reclaim_contig()
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On 04/10/2015 04:11, Svatopluk Kraus wrote:
> Hi,
>
> my RPI-B has been stuck in vm_reserv_reclaim_contig() due to a bug
> within that function. I can reproduce that easily on my two-core
> pandaboard when I limit all memory in system to 128MiB and run "make
> -j16 kernel-toolchain". It happens in few seconds.
>
> The patch should be self-explanatory. The problem is that there is a
> free page found in reservation which does not fulfill alignment
> requirement, thus next free page should be looked for. However, due to
> the bug, the same free page is found out again and again.
>
> The patch takes into account that shift by m on n-bit arch has an
> undefined behaviour if m >=3D n.
>

The patch looks correct.  I'm just going to tweak the comment, and then
I'll commit it.