From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1AB48811E2 for ; Tue, 30 Jan 2024 14:59:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706626794; cv=none; b=eoKsRxxuSRTOMwSsVxitSH+HqVJxW35kHABlrgnsaclRLLZ86n4IzTsbfxZ3mvTU7Up4lSmB5BmLh3CzKygZzeI1+fZy/uSuUjt6W+OSA5ktpuE5+bmVm8SVauwKAkMi1Mn8SBRxH0P3qJn73T7gcb3/ujJZZJK4I5zify37mtc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706626794; c=relaxed/simple; bh=1LuZkRPG9GzhfRFDPYw9OTIIQJewHWz9C37ilIbagKk=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=bBubJYN8HuF7EhXGUaJibsCMtrdcMfZUr3KH6Re/EucEnbmQeiZ3BRamew2tkQggUqbOYuIJEzOmKFiqEZmbLYUEN07Q8IYyNNlIYhs1vhHiNOoYyh+g4j2kx4mV42N/UXblM8ext95zLOmPIbOO0ArDkkcKvx/GDjdvKGQnYxk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=isSwE/xV; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="isSwE/xV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1000AC43390; Tue, 30 Jan 2024 14:59:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1706626793; bh=1LuZkRPG9GzhfRFDPYw9OTIIQJewHWz9C37ilIbagKk=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=isSwE/xVp7/LefQrYR1FbIxceZNSMIRNOTap7vVM6oO8LDZ1Y5JT9EWvcd1ZsDVrE 3K8cN9TyJIh8zAm/Lwcc/8MpbIqaofDMt8p9+BRbW1WT3o2PA9aUJpjV2h+faDJNlE eIgHrhgfEODU0in6/j019B5VC0ro8BQB+adGelXrQ8YsI01s+WRhC7HpJ5L8DfwCfr 8LW7pfp7QvEbrshWafiBPjFuF7ugKUqSndtU6lQhrFc+Yh4L34CHqrPBExTA+xJwC+ 1a3pw+qMvIVfjwbrp56XjYBFppMiNeDKkauh4IAFgYJrxVWtiyhQhuRm4VMFxLsChi uFpSksSNGeFDQ== Message-ID: Subject: Re: [PATCH] NFS: Fix nfs_netfs_issue_read() xarray locking for writeback interrupt From: Jeff Layton To: David Wysochanski Cc: David Howells , Anna Schumaker , Trond Myklebust , linux-nfs@vger.kernel.org, linux-cachefs@redhat.com Date: Tue, 30 Jan 2024 09:59:51 -0500 In-Reply-To: References: <20240129154750.1245317-1-dwysocha@redhat.com> <1526807.1706548521@warthog.procyon.org.uk> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxwn8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1WvegyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqVT2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtVYrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8snVluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQcDEsvv5IMmeMe1/qLZ6NaVkNuL3WOXvxaVT9USW1+/SGipO2IpKJjeDZfehlB/kpfF24+RrK+seQfCBYyUE8QJpvTZyfUHNYldXlrjO6n5MdOempLqWpfOmcGkwnyNRBR46g/jf8KnPRwXs509yAqDB6sELZH+yWr9LQZEwARAQABtCVKZWZmIExheXRvbiA8amxheXRvbkBwb29jaGllcmVkcy5uZXQ+iQI7BBMBAgAlAhsDBgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAUCTpXWPAIZAQAKCRAADmhBGVaCFc65D/4gBLNMHopQYgG/9RIM3kgFCCQV0pLv0hcg1cjr+bPI5f1PzJoOVi9s0wBDHwp8+vtHgYhM54yt43uI7Htij0RHFL5eFqoVT4TSfAg2qlvNemJEOY0e4daljjmZM7UtmpGs9NN0r9r50W82eb5Kw5bc/ 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 kZWuOsJdJQdmwlWC5L5ln9xgfr/4mOY38B0U= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 (3.50.3-1.fc39) Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2024-01-30 at 09:56 -0500, David Wysochanski wrote: > On Mon, Jan 29, 2024 at 12:44=E2=80=AFPM Jeff Layton = wrote: > >=20 > > On Mon, 2024-01-29 at 12:34 -0500, David Wysochanski wrote: > > > On Mon, Jan 29, 2024 at 12:15=E2=80=AFPM David Howells wrote: > > > >=20 > > > > Dave Wysochanski wrote: > > > >=20 > > > > > - xas_lock(&xas); > > > > > + xas_lock_irqsave(&xas, flags); > > > > > xas_for_each(&xas, page, last) { > > > >=20 > > > > You probably want to use RCU, not xas_lock(). The pages are locked= and so > > > > cannot be evicted from the xarray. > > > >=20 > > >=20 > > > I tried RCU originally and ran into a problem because NFS can schedul= e > > > (see comment on line 328 below) > > >=20 > > > 326 xas_lock_irqsave(&xas, flags); > > > 327 xas_for_each(&xas, page, last) { > > > 328 /* nfs_read_add_folio() may schedule() due to pNF= S > > > layout and other RPCs */ > > > 329 xas_pause(&xas); > > > 330 xas_unlock_irqrestore(&xas, flags); > > > 331 err =3D nfs_read_add_folio(&pgio, ctx, page_folio= (page)); > > > 332 if (err < 0) { > > > 333 netfs->error =3D err; > > > 334 goto out; > > > 335 } > > > 336 xas_lock_irqsave(&xas, flags); > > > 337 } > > > 338 xas_unlock_irqrestore(&xas, flags); > > >=20 > >=20 > > Looking at it more closely, I think you might want to just use > > xa_for_each_start(). That will do the traversal using the rcu_read_lock > > under the hood, and you should be able to block on every iteration. > >=20 > Thanks Jeff. Yes, I agree after looking at this further, this is a > good approach, and much cleaner. I'll work on a v2 patch (actually > with xa_for_each_range as you suggested off list) and send after > a bit of testing -- so far, so good. >=20 > FWIW, my original usage of RCU was outside the whole loop. > I ran into problems due to nfs_read_add_folio(). >=20 Makes sense. In principle you could do this by just dropping and acquiring the rcu_read_lock in the same places you do the spinlock in the original patch, but using xa_for_each_range is much simpler. --=20 Jeff Layton