Re: [PATCH 2.5.66-mm2] Fix page_convert_anon locking issues

[Dave McCracken <dmccr@us.ibm.com>]

--On Wednesday, April 02, 2003 15:09:03 -0800 Andrew Morton
<akpm@digeo.com> wrote:

> i_shared_sem won't stop that.  The pte points into thin air, and may now
> point at a value which looks like our page.

Once we find a match in the pte entry, we have the additional protection of
the pte_chain lock.  The pte entry is never cleared without a call to
page_remove_rmap, which will block on the pte_chain lock.

>> Because the page is in transition from !PageAnon to PageAnon.
> 
> These are file-backed pages.  So what does PageAnon really mean?

I suppose PageAnon should be renamed to PageChain, to mean it's using
pte_chains.  It did mean anon pages until I used it for nonlinear pages.

>> We have to
>> hold the pte_chain lock during the entire transition in case someone else
>> tries to do something like page_remove_rmap, which would break.
> 
> How about setting PageAnon at the _start_ of the operation? 
> page_remove_rmap() will cope with that OK.

Hmm... I was gonna say that page_remove_rmap will BUG() if it doesn't find
the entry, but it's only under DEBUG and could easily be changed.  Lemme
think on this one a bit.  I need to assure myself it's safe to go unlocked
in the middle.

Dave

======================================================================
Dave McCracken          IBM Linux Base Kernel Team      1-512-838-3059
dmccr@us.ibm.com                                        T/L   678-3059

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