From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 12BB7ECAAD1 for ; Thu, 1 Sep 2022 10:56:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234367AbiIAK4N (ORCPT ); Thu, 1 Sep 2022 06:56:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53498 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234364AbiIAKzq (ORCPT ); Thu, 1 Sep 2022 06:55:46 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 18BFB53D02 for ; Thu, 1 Sep 2022 03:55:13 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 9075C6192C for ; Thu, 1 Sep 2022 10:55:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4E502C433D6; Thu, 1 Sep 2022 10:55:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1662029712; bh=g+5KI90pFtobCBKWjqqMcvyULX6IvSj3TDV2ovmnpY8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=AdVa5rLBR1euPCySHLIKa8fPv8vaYvcdjIVBrJzV/lcfXW4E2Q0K09EiIeFxG80gC r+9HiP+y31HB6bHSC8dJNR8nfxZL0VtwfNPY2ZFbDmOtugQtQsDRFqL72prRm3gD0A rGht13ZpzjhGdz8rsFcQrb8ix3L3gGPzGNk3Hl93RV7PwZstMtsZKPMblT+6FY9IWN rfOJC8VIkrDtZcn4KjJSO5i9cm4HvY6dyBKG5u/iJXiiI5FP3BgnjgEcmevfs6Wlpy BOyw/d2aKf0Ums1s46MykAQUQgLKICjjnDFaYvzMBQakMqEodouY2lV4E6MOGEzkC9 oo2H0XrYhKkwg== Date: Thu, 1 Sep 2022 12:55:08 +0200 From: Carlos Maiolino To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org Subject: Re: [ANNOUNCE] xfsprogs for-next updated Message-ID: <20220901105508.kg5nu7xet6ylujcz@andromeda> References: <20220830115220.5s2nlztp56fbf4xa@andromeda> <20220831094325.5dwjygbcd5mcibok@andromeda> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org > > Oh, the usual problems of adding a new interface... > > 1. Who is responsible for setting m_sb_bp? > > Should libxfs_mount attach m_sb_bp? Should individual programs decide > to do that if they require the functionality? Should we instead have a > xfs_getsb function that returns m_sb_bp if set, or libxfs_getbufr's a > new buffer and tries to cmpxchg it with the pointer? > > What about mkfs, which needs to libxfs_mount before it's even written > anything to disk? > > 2. Should it be a cached buffer so that any other program (e.g. xfs_db) > doing open-coded accesses of the superblock will get the same cached > buffer, or should it be uncached like the kernel? > > If we decide on uncached, this will necessitate a full audit of xfsprogs > to catch open-coded calls to libxfs_getbuf for the primary super, or > else coherency problems will result. > > If we decide on using a cached buffer and setting it in libxfs_mount, > then the part of xfs_repair that tears down the buffer cache and > reinitializes it with a different hash size will also have to learn to > brelse m_sb_bp before destroying the cache and re-assign it afterwards. > Alternately, I suppose it could learn to rehash itself. > > This is a /lot/ to think about to solve one problem in one program. Yeah, I do agree. Maybe it's better to go with your initial idea for 6.0, and we postpone the SB buffer pinning to a later release avoiding people to hit this issue ASAP?! > > > I didn't have time to try to reproduce those deadlocks yet though. > > If you modify cache_node_get like this to make reclaim more aggressive: > > diff --git a/libxfs/cache.c b/libxfs/cache.c > index 139c7c1b..b5e1bcf8 100644 > --- a/libxfs/cache.c > +++ b/libxfs/cache.c > @@ -448,10 +448,10 @@ cache_node_get( > /* > * not found, allocate a new entry > */ > + priority = cache_shake(cache, priority, false); > node = cache_node_allocate(cache, key); > if (node) > break; > - priority = cache_shake(cache, priority, false); > /* > * We start at 0; if we free CACHE_SHAKE_COUNT we get > * back the same priority, if not we get back priority+1. > > It's trivially reproducible with xfs_repair (do not specify -n). Thanks, I'm gonna try it :) > > --D > > > > > > > [1] https://lore.kernel.org/linux-xfs/166007921743.3294543.7334567013352169774.stgit@magnolia/ > > > [2] https://lore.kernel.org/linux-xfs/20220811221541.GQ3600936@dread.disaster.area/ > > > > -- > > Carlos Maiolino -- Carlos Maiolino