Subject: Re: bio linked list corruption.
To: Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>
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CC: Dave Jones <davej@codemonkey.org.uk>,
        Andy Lutomirski <luto@kernel.org>, Jens Axboe <axboe@fb.com>,
        Al Viro <viro@zeniv.linux.org.uk>, Josef Bacik <jbacik@fb.com>,
        David Sterba <dsterba@suse.com>,
        linux-btrfs <linux-btrfs@vger.kernel.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>
From: Chris Mason <clm@fb.com>
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Date: Mon, 24 Oct 2016 18:02:35 -0400
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On 10/24/2016 05:50 PM, Linus Torvalds wrote:
> On Mon, Oct 24, 2016 at 2:17 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>> The vmalloc/vfree code itself is a bit scary. In particular, we have a
>> rather insane model of TLB flushing. We leave the virtual area on a
>> lazy purge-list, and we delay flushing the TLB and actually freeing
>> the virtual memory for it so that we can batch things up.
>
> Never mind. If DaveJ is running with DEBUG_PAGEALLOC, then the code in
> vmap_debug_free_range() should have forced a synchronous TLB flush fro
> vmalloc ranges too, so that doesn't explain it either.
>

My big fear here is that we're just triggering an old stack corruption 
more reliably.  I wonder if we can make it happen much faster by 
restricting the stacks to a static list and cycling through them in lifo 
fashion?

-chris