From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 25 May 2004 21:08:10 -0700 (PDT) From: Linus Torvalds Subject: Re: [PATCH] ppc64: Fix possible race with set_pte on a present PTE In-Reply-To: <1085541906.14969.412.camel@gaston> Message-ID: References: <1085369393.15315.28.camel@gaston> <1085371988.15281.38.camel@gaston> <1085373839.14969.42.camel@gaston> <20040525034326.GT29378@dualathlon.random> <20040525114437.GC29154@parcelfarce.linux.theplanet.co.uk> <20040525153501.GA19465@foobazco.org> <20040525102547.35207879.davem@redhat.com> <20040525105442.2ebdc355.davem@redhat.com> <1085521251.24948.127.camel@gaston> <1085522860.15315.133.camel@gaston> <1085530867.14969.143.camel@gaston> <1085541906.14969.412.camel@gaston> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Benjamin Herrenschmidt Cc: "David S. Miller" , wesolows@foobazco.org, willy@debian.org, Andrea Arcangeli , Andrew Morton , Linux Kernel list , mingo@elte.hu, bcrl@kvack.org, linux-mm@kvack.org, Linux Arch list List-ID: On Wed, 26 May 2004, Benjamin Herrenschmidt wrote: > > I think we are using ptep_establish for more than just setting those > 2 bits (like for setting up the new PTE in break_cow and such while > the current implementationL/definition is more like just setting > those bits and nothing else.... You're right. We do use it on the do_wp_page() path, and there we actually use a whole new page in the "break_cow()" case. That case is in fact fundamentally different from the other ones. So we should probably break up the "ptep_establish()" into its two pieces, since the callers don't actually want to do the same thing. One really wants to do a "clear old one, set a totally new one", and the two other places want to actually update just the dirty and accessed bits. In fact, the only non-generic user of "ptep_establish()" (s390) didn't want to use the generic version exactly because of this very conceptual bug. It uses "ptep_clear_flush()" for the replacement case, which actually makes sense. So does it work if you do this appended patch first? This is a real cleanup, and I think it will allow us to get rid of the s390-specific code in ptep_establish(). Along with hopefully fixing your problem too. After this, we should be able to have a BUG() in "set_pte()" if the entry wasn't clear before (assuming the arch doesn't use set_pte() for the dirty updates etc). Linus --- ===== mm/memory.c 1.177 vs edited ===== --- 1.177/mm/memory.c Tue May 25 12:37:09 2004 +++ edited/mm/memory.c Tue May 25 21:04:49 2004 @@ -1004,7 +1004,10 @@ flush_cache_page(vma, address); entry = maybe_mkwrite(pte_mkdirty(mk_pte(new_page, vma->vm_page_prot)), vma); - ptep_establish(vma, address, page_table, entry, 1); + + /* Get rid of the old entry, replace with new */ + ptep_clear_flush(vma, address, page_table); + set_pte(page_table, entry); update_mmu_cache(vma, address, entry); } -- 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