From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 2 Apr 2003 13:29:39 -0800 From: Andrew Morton Subject: Re: [PATCH 2.5.66-mm2] Fix page_convert_anon locking issues Message-Id: <20030402132939.647c74a6.akpm@digeo.com> In-Reply-To: <8910000.1049303582@baldur.austin.ibm.com> References: <8910000.1049303582@baldur.austin.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Dave McCracken Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: Dave McCracken wrote: > > > I came up with a scheme for accessing the page tables in page_convert_anon > that should work without requiring locks. Hugh has looked at it and agrees > it addresses the problems he found. Anyway, here's the patch. > I am unable to convince myself that this is correct. It's playing with pmd and pte pages which can be freed, reallocated and filled with random stuff. I really don't see how that can work, but am willing to be taught. Because we hold i_shared_sem we know that the pgd layer is stable and that the mm's aren't going away. Is it not possible to take each mm's page_table_lock? There's a ranking problem with pte_chain_lock(), but that can presumably be resolved by doing a trylock on the page_table_lock and if that fails, restart the whole operation. But then again, why is it not possible to just do: list_for_each_entry(vma, &mapping->i_mmap, shared) { if (!pte_chain) pte_chain = pte_chain_alloc(GFP_KERNEL); spin_lock(&mm->page_table_lock); pte = find_pte(vma, page, NULL); if (pte) pte_chain = page_add_rmap(page, pte, pte_chain); spin_unlock(&mm->page_table_lock); } pte_chain_free(pte_chain); up(&mapping->i_shared_sem); ? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org