From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4533AF6C.6020207@yahoo.com.au> Date: Tue, 17 Oct 2006 02:12:28 +1000 From: Nick Piggin MIME-Version: 1.0 Subject: Re: pagefault_disable (was Re: [patch 6/6] mm: fix pagecache write deadlocks) References: <20061013143516.15438.8802.sendpatchset@linux.site> <20061013143616.15438.77140.sendpatchset@linux.site> <1160912230.5230.23.camel@lappy> <20061015115656.GA25243@wotan.suse.de> <1160920269.5230.29.camel@lappy> <20061015141953.GC25243@wotan.suse.de> <1160927224.5230.36.camel@lappy> <20061015155727.GA539@wotan.suse.de> <1160928835.5230.41.camel@lappy> <4533A411.2020207@yahoo.com.au> <1161014732.2096.9.camel@taijtu> In-Reply-To: <1161014732.2096.9.camel@taijtu> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Peter Zijlstra Cc: Linux Memory Management , Linux Kernel , Andrew Morton , David Howells , Ingo Molnar List-ID: Peter Zijlstra wrote: > On Tue, 2006-10-17 at 01:24 +1000, Nick Piggin wrote: >>Also, the rest of the kernel tree (mainly uaccess and futexes) should be >>converted ;) > > > Yeah, lotsa places to touch. > > >>>Index: linux-2.6/mm/filemap.h >>>=================================================================== >>>--- linux-2.6.orig/mm/filemap.h 2006-10-14 20:20:20.000000000 +0200 >>>+++ linux-2.6/mm/filemap.h 2006-10-15 17:17:45.000000000 +0200 >>>@@ -21,6 +21,22 @@ __filemap_copy_from_user_iovec_inatomic( >>> size_t bytes); >>> >>> /* >>>+ * By increasing the preempt_count we make sure the arch preempt >>>+ * handler bails out early, before taking any locks, so that the copy >>>+ * operation gets terminated early. >>>+ */ >>>+pagefault_static inline void disable(void) >>>+{ >>>+ inc_preempt_count(); > > > I think we also need a barrier(); here. We need to make sure the preempt > count is written to memory before we hit the fault handler. It will come from this thread, but I guess the fault is not an event the compiler can forsee, so indeed it might optimise this into the wrong place. Perhaps not with any copy*user implementation we have, but at least in theory... >>>+pagefault_static inline void enable(void) >>>+{ >>>+ dec_preempt_count(); >>>+ preempt_check_resched(); >>>+} You'll want barriers before and after the dec_preempt_count, for similar reasons. -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com -- 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: email@kvack.org