From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tvrtko Ursulin Subject: Re: [FIXES 1/3] drm/i915/userptr: Try to acquire the page lock around set_page_dirty() Date: Mon, 11 Nov 2019 14:12:33 +0000 Message-ID: References: <20191111133205.11590-1-chris@chris-wilson.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20191111133205.11590-1-chris@chris-wilson.co.uk> Content-Language: en-US Sender: stable-owner@vger.kernel.org To: Chris Wilson , intel-gfx@lists.freedesktop.org Cc: joonas.lahtinen@linux.intel.com, Lionel Landwerlin , Tvrtko Ursulin , stable@vger.kernel.org List-Id: intel-gfx@lists.freedesktop.org On 11/11/2019 13:32, Chris Wilson wrote: > set_page_dirty says: > > For pages with a mapping this should be done under the page lock > for the benefit of asynchronous memory errors who prefer a > consistent dirty state. This rule can be broken in some special > cases, but should be better not to. > > Under those rules, it is only safe for us to use the plain set_page_dirty > calls for shmemfs/anonymous memory. Userptr may be used with real > mappings and so needs to use the locked version (set_page_dirty_lock). > > However, following a try_to_unmap() we may want to remove the userptr and > so call put_pages(). However, try_to_unmap() acquires the page lock and > so we must avoid recursively locking the pages ourselves -- which means > that we cannot safely acquire the lock around set_page_dirty(). Since we > can't be sure of the lock, we have to risk skip dirtying the page, or > else risk calling set_page_dirty() without a lock and so risk fs > corruption. > > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203317 > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112012 > Fixes: 5cc9ed4b9a7a ("drm/i915: Introduce mapping of user pages into video m > References: cb6d7c7dc7ff ("drm/i915/userptr: Acquire the page lock around set_page_dirty()") > References: 505a8ec7e11a ("Revert "drm/i915/userptr: Acquire the page lock around set_page_dirty()"") > References: 6dcc693bc57f ("ext4: warn when page is dirtied without buffers") > Signed-off-by: Chris Wilson > Cc: Lionel Landwerlin > Cc: Tvrtko Ursulin > Cc: Joonas Lahtinen > Cc: stable@vger.kernel.org > --- > drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 22 ++++++++++++++++++++- > 1 file changed, 21 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c > index ee65c6acf0e2..dd104b0e2071 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c > @@ -646,8 +646,28 @@ i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj, > obj->mm.dirty = false; > > for_each_sgt_page(page, sgt_iter, pages) { > - if (obj->mm.dirty) > + if (obj->mm.dirty && trylock_page(page)) { > + /* > + * As this may not be anonymous memory (e.g. shmem) > + * but exist on a real mapping, we have to lock > + * the page in order to dirty it -- holding > + * the page reference is not sufficient to > + * prevent the inode from being truncated. > + * Play safe and take the lock. > + * > + * However...! > + * > + * The mmu-notifier can be invalidated for a > + * migrate_page, that is alreadying holding the lock > + * on the page. Such a try_to_unmap() will result > + * in us calling put_pages() and so recursively try > + * to lock the page. We avoid that deadlock with > + * a trylock_page() and in exchange we risk missing > + * some page dirtying. > + */ > set_page_dirty(page); > + unlock_page(page); > + } > > mark_page_accessed(page); > put_page(page); > It looks that the bug report could be about BUG_ON(PageWriteback(page)) in ext4/mpage_prepare_extent_to_map which would be somewhat consistent with not being allowed to call set_page_dirty on an unlocked page. So on the basis of that: Reviewed-by: Tvrtko Ursulin Regards, Tvrtko 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 X-Spam-Level: X-Spam-Status: No, score=-7.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, HK_RANDOM_FROM,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ADB67C17445 for ; Mon, 11 Nov 2019 14:12:40 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8D7E521D7F for ; Mon, 11 Nov 2019 14:12:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8D7E521D7F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 323E26E919; Mon, 11 Nov 2019 14:12:40 +0000 (UTC) Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by gabe.freedesktop.org (Postfix) with ESMTPS id 5D5FA6E21D for ; Mon, 11 Nov 2019 14:12:39 +0000 (UTC) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Nov 2019 06:12:37 -0800 X-IronPort-AV: E=Sophos;i="5.68,293,1569308400"; d="scan'208";a="197679382" Received: from mpotanix-mobl2.ccr.corp.intel.com (HELO [10.252.20.183]) ([10.252.20.183]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/AES256-SHA; 11 Nov 2019 06:12:35 -0800 To: Chris Wilson , intel-gfx@lists.freedesktop.org References: <20191111133205.11590-1-chris@chris-wilson.co.uk> From: Tvrtko Ursulin Organization: Intel Corporation UK Plc Message-ID: Date: Mon, 11 Nov 2019 14:12:33 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191111133205.11590-1-chris@chris-wilson.co.uk> Content-Language: en-US Subject: Re: [Intel-gfx] [FIXES 1/3] drm/i915/userptr: Try to acquire the page lock around set_page_dirty() X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: stable@vger.kernel.org Content-Transfer-Encoding: base64 Content-Type: text/plain; charset="utf-8"; Format="flowed" Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Message-ID: 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