From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 10 Oct 2006 07:22:48 +0200 From: Nick Piggin Subject: Re: [patch] mm: bug in set_page_dirty_buffers Message-ID: <20061010052248.GB24600@wotan.suse.de> References: <20061009202039.b6948a93.akpm@osdl.org> <20061010033412.GH15822@wotan.suse.de> <20061009205030.e247482e.akpm@osdl.org> <20061010035851.GK15822@wotan.suse.de> <20061009211404.ad112128.akpm@osdl.org> <20061010042144.GM15822@wotan.suse.de> <20061009213806.b158ea82.akpm@osdl.org> <20061010044745.GA24600@wotan.suse.de> <20061009220127.c4721d2d.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20061009220127.c4721d2d.akpm@osdl.org> Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: Linus Torvalds , Peter Zijlstra , Linux Memory Management List , Greg KH List-ID: On Mon, Oct 09, 2006 at 10:01:27PM -0700, Andrew Morton wrote: > On Tue, 10 Oct 2006 06:47:45 +0200 > Nick Piggin wrote: > > > There we can trylock all the pages and bale if any fail. > > > > Hmm, try_to_unmap is OK because the page is already locked. page_remove_rmap > > isn't allowed to fail. > > I was talking about try_to_unmap_cluster(). But page_remove_rmap's many callers are still screwed. Take do_wp_page, for example. > > > But where? locking the page is the preferred way to solve this stuff. > > > (Well, locking the buffers might work, but isn't needed, and locking the > > > page covers other stuff) > > > > AFAIKS, it is just fs/buffer.c that is racy. > > Need to review all ->set_page_dirty, ->writepage, ->invalidatepage, ->etc > implementations before we can say that. > > > Why can't it use > > mapping->private_lock or the buffer bit spinlock? > > block_invalidatepage() wants to do lock_buffer(). > > It can probably be made to work. But a sane interface is "when dinking > with page internals, lock the page". I disagree because it will lead to horrible hacks because many callers can't sleep. If anything I would much prefer an innermost-spinlock in page->flags that specifically excludes truncate. Actually tree_lock can do that now, provided we pin mapping in all callers to set_page_dirty (which we should do). Then the locking protocol is up to fs/buffer.c. You could set a bit in the buffer "BH_Invalidated" in truncate before clearing dirty, and test for that bit in set_page_dirty_buffers? -- 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