Re: 3rd version of R/W mmap_sem patch available

[Andrew Morton <andrewm@uow.edu.au>]

Linus Torvalds wrote:
> 
> There is a 2.4.3-pre5 in the test-directory on ftp.kernel.org.
> 

I stared long and hard at expand_stack().  Its first access
to vma->vm_start appears to be safe wrt other threads which 
can alter this, but perhaps the page_table_lock should be
acquired earlier here?



We now have:

	free_pgd_slow();
	pmd_free_slow();
	pte_free_slow();

Could we please have consistent naming back?



in do_wp_page():

        spin_unlock(&mm->page_table_lock);
        new_page = alloc_page(GFP_HIGHUSER);
        if (!new_page)
                return -1;
        spin_lock(&mm->page_table_lock);

Should retake the spinlock before returning.



General comment: an expensive part of a pagefault
is zeroing the new page.  It'd be nice if we could
drop the page_table_lock while doing the clear_user_page()
and, if possible, copy_user_page() functions.  Very nice.




read_zero_pagealigned()->zap_page_range()

	The handling of mm->rss is racy.  But I think
	it always has been?




This comment in mprotect.c:
+       /* XXX: maybe this could be down_read ??? - Rik */

I don't think so.  The decisions about where in the 
vma tree to place the new vma would be unprotected and racy.



Apart from that - I looked at it (x86-only) very closely and
it seems solid.
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