Messages in this thread | | | Date | Thu, 15 Sep 2005 17:47:02 +0200 | From | Andrea Arcangeli <> | Subject | Re: ptrace can't be transparent on readonly MAP_SHARED |
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On Thu, Sep 15, 2005 at 08:12:59AM -0700, Linus Torvalds wrote: > have a PROT_READONLY/PROT_NONE area that is visible from the debugger, but > continues to cause SIGSEGV's if the user process itself tries to access > it. To me, that's good.
Continue to cause sigsegv yes, but on the wrong page, when it will read the page it can contain different data compared to what is on disk/pagecache.
> There would have to be some real advantage to _not_ doing what we're doing > now. And I don't see an advantage.
The advantage is a faster fast path and less special cases to keep in mind.
> The real complexity is not "maybe_mkwrite()", which is trivial. The real
It is trivial yes, but for it to work without deadlocks, it requires non-trivial changes to the page fault handler and get_user_pages.
I guess this is mostly a matter of taste, but my taste is about keeping it simple and fast (though the difference is certainly not measurable).
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