From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755186Ab0C1UHk (ORCPT ); Sun, 28 Mar 2010 16:07:40 -0400 Received: from moutng.kundenserver.de ([212.227.17.10]:57121 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755146Ab0C1UHj (ORCPT ); Sun, 28 Mar 2010 16:07:39 -0400 From: Arnd Bergmann To: Stefan Richter Subject: Re: [GIT, RFC] Killing the Big Kernel Lock Date: Sun, 28 Mar 2010 21:05:50 +0100 User-Agent: KMail/1.12.2 (Linux/2.6.31-19-generic; KDE/4.3.2; x86_64; ; ) Cc: Jiri Kosina , Frederic Weisbecker , linux-kernel@vger.kernel.org, Matthew Wilcox , Thomas Gleixner , jblunck@suse.de, Alan Cox , Ingo Molnar , John Kacur References: <201003242240.54907.arnd@arndb.de> <201003271537.40488.arnd@arndb.de> <4BAF4B49.9070308@s5r6.in-berlin.de> In-Reply-To: <4BAF4B49.9070308@s5r6.in-berlin.de> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201003282205.50886.arnd@arndb.de> X-Provags-ID: V01U2FsdGVkX18sgZDGNzbQo6Hgq2l64uLdNpxol++3t9u6emd TDFS0Wt1qcEhe+ylNHcyvN1Dji8O6+K72UNwYMF0H2sNS3FrzM WLaGTJuTrfkIBWk1bqgiw== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sunday 28 March 2010, Stefan Richter wrote: > Arnd Bergmann wrote: > > Your patches look good, but it would be helpful to also set .llseek = no_llseek > > in the file operations, because that is much easier to grep for than > > only the nonseekable_open. While it's technically a NOP on the presence of > > nonseekable_open, it will help that I don't accidentally apply my patch on > > top of yours. > > Sounds like a plan, but (a) if my .llseek = no_llseek and your .llseek = > default_llseek are not within diff context range, you (or whoever else > merges mine and yours) only get a compiler warning (Initializer entry > defined twice) rather than a merge conflict which couldn't be missed, > (b) there won't be a merge conflict in "BKL removal: mark remaining > users as 'depends on BKL'". (c) While I don't mind adding more visual > clutter to ieee1394/*, I prefer terse coding in firewire/*. > > How about I put my nonseekable_open additions into a release branch and > send you a pull request after a few days exposure in linux-next? If you > do not plan to respin your patch queue soon or at all, I could even let > you pull a for-arnd branch with a semantically correct merge of yours > and mine. I can probably remember this specific one now, but for other people doing the same on their subsystems, adding no_llseek may help reduce the need for coordination. > General thoughts: > > ".llseek = NULL," so far meant "do the Right Thing on lseek() and > friends, as far as the fs core can tell". Shouldn't we keep it that > way? It's as close to other ".method = NULL," as it can get, which > either mean "silently skip this method if it doesn't matter" (e.g. > .flush) or "fail attempts to use this method with a fitting errno" (e.g. > .write). My series changes the default from 'default_llseek' to 'generic_file_llseek', which is almost identical, except for taking the inode mutex instead of the BKL. Another option that has been discussed before is to make no_llseek the default, but that might cause more serious problems wiht drivers that really require seeking. Since using default_llseek can only ever make a difference if the driver actually uses the BKL in any other function, I could go through the patches again and revert those that do no use the BKL anywhere else. > Of course, as we have already seen with infiniband, firewire, ieee1394, > .llseek = NULL is ambiguous in practice. Does the driver really want to > use default_llseek, or should it rather use no_llseek and/or > nonseekable_open, or should it even implement a dummy_llseek() { return > 0; } which avoids the BKL but preserves ABI behaviour? This needs to be > resolved for each and every case eventually, regardless of whether or > when your addition of .llseek = default_llseek enters mainline. Yes, that also sounds like a good idea. I believe that Jan actually posted a patch to do that at some point. Arnd