From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 11 Oct 2006 18:57:18 +0200 From: Nick Piggin Subject: Re: SPAM: Re: [patch 2/5] mm: fault vs invalidate/truncate race fix Message-ID: <20061011165717.GB5259@wotan.suse.de> References: <20061010121314.19693.75503.sendpatchset@linux.site> <20061010121332.19693.37204.sendpatchset@linux.site> <20061010213843.4478ddfc.akpm@osdl.org> <452C838A.70806@yahoo.com.au> <20061010230042.3d4e4df1.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org Return-Path: To: Linus Torvalds Cc: Andrew Morton , Nick Piggin , Linux Memory Management , Linux Kernel List-ID: On Wed, Oct 11, 2006 at 09:21:16AM -0700, Linus Torvalds wrote: > > > On Tue, 10 Oct 2006, Andrew Morton wrote: > > > > On Wed, 11 Oct 2006 15:39:22 +1000 > > Nick Piggin wrote: > > > > > But I see that it does read twice. Do you want that behaviour retained? It > > > seems like at this level it would be logical to read it once and let lower > > > layers take care of any retries? > > > > argh. Linus has good-sounding reasons for retrying the pagefault-path's > > read a single time, but I forget what they are. Something to do with > > networked filesystems? (adds cc) > > Indeed. We _have_ to re-try a failed IO that we didn't start ourselves. > > The original IO could have been started by a person who didn't have > permissions to actually carry it out successfully, so if you enter with > the page locked (because somebody else started the IO), and you wait for > the page and it's not up-to-date afterwards, you absolutely _have_ to try > the IO, and can only return a real IO error after your _own_ IO has > failed. Sure, but we currently try to read _twice_, don't we? > There is another issue too: even if the page was marked as having an error > when we entered (and no longer locked - maybe the IO failed last time > around), we should _still_ re-try. It might be a temporary error that has > since gone away, and if we don't re-try, we can end up in the totally > untenable situation where the kernel makes a soft error into a hard one. Yes, and in that case I think the page should be !Uptodate, so no problem there. -- 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