Re: [PATCH 2.5.42-mm3] Fix mremap for shared page tables

[Hugh Dickins <hugh@veritas.com>]

On Tue, 15 Oct 2002, Dave McCracken wrote:
> 
> Hugh Dickens was right.  mremap was broken wrt shared page tables.
           i

Sorry, Dave, I only mentioned mremap as one _example_.  You have
changed the locking rules for ptes in page tables in two or three
sources, but there's a number more which need to be updated too.

Please don't ask me to list which, it's a matter of looking at all
the uses of ->page_table_lock and whether those places need to be
changed to fit the new locking scheme - some of the uses are quite
irrelevant, some may be obscure, some may be historic, some must
be changed.

I wouldn't mind if it was just broken wrt shared page tables,
CONFIG_SHAREPTE is easily made experimental.  But the locking rules
have (rightly) been changed in all cases, so -mm tree is now unsafe.
A stopgap measure might be to hold on to page_table_lock for as
long as before, then fix sources up piecemeal - but that approach
would still leave CONFIG_SHAREPTE y broken for a while.

Let me say again, that I have _not_ actually observed any problem
yet: we're talking about races and correctness, I don't mean to be
alarmist.

Hugh

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