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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0D0ADC54EE9 for ; Tue, 20 Sep 2022 08:42:40 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4FEA9940008; Tue, 20 Sep 2022 04:42:40 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4AE45940007; Tue, 20 Sep 2022 04:42:40 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 34F50940008; Tue, 20 Sep 2022 04:42:40 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 258EC940007 for ; Tue, 20 Sep 2022 04:42:40 -0400 (EDT) Received: from smtpin28.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id F3D6440C7F for ; Tue, 20 Sep 2022 08:42:39 +0000 (UTC) X-FDA: 79931822838.28.623A30D Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by imf27.hostedemail.com (Postfix) with ESMTP id 8611140002 for ; Tue, 20 Sep 2022 08:42:39 +0000 (UTC) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id ED52A1F898; Tue, 20 Sep 2022 08:42:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1663663357; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VIiaZw8kyqLy+k7/L0lKws/bc45zpwA5196SAUlqTnE=; b=WhWdox47SVo2w033FWXOrKg4uJsJ6QizXju5q9h/4jzaYV8ks9I4eN+TT2KfxCtxL94d0i mNLY29nzm2AgHF5XYQhRvzfBETyTbtFKvcbcJYM6APTbCrjauOYYtwnWiJi+DGvoUinlIL Mawd1xVO96D1gzT1UtAa3vCdhmPuO48= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1663663357; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VIiaZw8kyqLy+k7/L0lKws/bc45zpwA5196SAUlqTnE=; b=s/4W4QsI7MIf3DbvvNSN4Q1jXe4XzTNY7nKe7NOHSDEdhww6/O7rMGlwb6E5fvAfql+YmC sW/6+WTFjlYI6ZDQ== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id B2FEF13ABB; Tue, 20 Sep 2022 08:42:37 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id MYoFK/18KWOmcAAAMHmgww (envelope-from ); Tue, 20 Sep 2022 08:42:37 +0000 Message-ID: <21646f5c-39ee-a51c-f30c-272de85ee350@suse.cz> Date: Tue, 20 Sep 2022 10:42:37 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Subject: Re: [PATCH] mm: Make failslab writable again Content-Language: en-US To: Alexander Atanasov , Jonathan Corbet , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: kernel@openvz.org, Kees Cook , Roman Gushchin , Jann Horn , Vijayanand Jitta , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20220920082033.1727374-1-alexander.atanasov@virtuozzo.com> From: Vlastimil Babka In-Reply-To: <20220920082033.1727374-1-alexander.atanasov@virtuozzo.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1663663359; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=VIiaZw8kyqLy+k7/L0lKws/bc45zpwA5196SAUlqTnE=; b=eswkzloG82+rE46jX8LtMlxLoaNK3TgwiKrdmvOP24ezZnkjyDn521rZ9GKJnPxp+6fQDU 5XTIXJgETKNxkujt1OlW+DFFe5oMzsZ3mQ2sa94Jt3gtmlB0jeVsyh3w4jXT+WDVf8B3ob tMQmIPCaVpD4BDXLs9MN8fVulTyo+Pk= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=WhWdox47; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b="s/4W4QsI"; dmarc=none; spf=pass (imf27.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.29 as permitted sender) smtp.mailfrom=vbabka@suse.cz ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1663663359; a=rsa-sha256; cv=none; b=qaykxIWhch2VS1VY0nunhnHMqm4XL+zb/reqTEgVmTTEWFbKBli3E8gwo5d4BejbCpNh8P n4peOb2ozfY26AictAvo0QvJpf06Fa3sfHFD/8fF9BQIZGmsDoIO2BDVWebvr4k8dfdHms 69I9/CswqC1EERb7aQioEDA+nerqsgs= X-Stat-Signature: mb57h76ta8z9wbgf546gnsn7q4y4yazf X-Rspamd-Queue-Id: 8611140002 Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=WhWdox47; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b="s/4W4QsI"; dmarc=none; spf=pass (imf27.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.29 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1663663359-213824 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 9/20/22 10:20, Alexander Atanasov wrote: > In (060807f841ac mm, slub: make remaining slub_debug related attributes > read-only failslab) it was made RO. "read-only) failslab was made RO" ? > I think it became a collateral victim to the other two options > (sanity_checks and trace) for which the reasons are perfectly valid. The commit also mentioned that modifying the flags is not protected in any way, see below. > Here is why: > - sanity_checks and trace are slab internal debug options, > failslab is used for fault injection. > - for fault injections, which by presumption are random, it > does not matter if it is not set atomically. You need to > set atleast one more option to trigger fault injection. > - in a testing scenario you may need to change it at runtime > example: module loading - you test all allocations limited > by the space option. Then you move to test only your module's > own slabs. > - when set by command line flags it effectively disables all > cache merges. > > Cc: Vlastimil Babka > Cc: Andrew Morton > Cc: Kees Cook > Cc: Roman Gushchin > Cc: Christoph Lameter > Cc: Jann Horn > Cc: Vijayanand Jitta > Cc: David Rientjes > Cc: Joonsoo Kim > Cc: Pekka Enberg > Link: http://lkml.kernel.org/r/20200610163135.17364-5-vbabka@suse.cz > > Signed-off-by: Alexander Atanasov > --- > Documentation/mm/slub.rst | 2 ++ > mm/slub.c | 14 +++++++++++++- > 2 files changed, 15 insertions(+), 1 deletion(-) > > diff --git a/Documentation/mm/slub.rst b/Documentation/mm/slub.rst > index 43063ade737a..86837073a39e 100644 > --- a/Documentation/mm/slub.rst > +++ b/Documentation/mm/slub.rst > @@ -116,6 +116,8 @@ options from the ``slub_debug`` parameter translate to the following files:: > T trace > A failslab > > +failslab file is writable, so writing 1 or 0 will enable or disable > +the option at runtime. Write returns -EINVAL if cache is an alias. > Careful with tracing: It may spew out lots of information and never stop if > used on the wrong slab. > > diff --git a/mm/slub.c b/mm/slub.c > index 862dbd9af4f5..7c15d312e0fb 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5617,7 +5617,19 @@ static ssize_t failslab_show(struct kmem_cache *s, char *buf) > { > return sysfs_emit(buf, "%d\n", !!(s->flags & SLAB_FAILSLAB)); > } > -SLAB_ATTR_RO(failslab); > + > +static ssize_t failslab_store(struct kmem_cache *s, const char *buf, > + size_t length) > +{ > + if (s->refcount > 1) > + return -EINVAL; > + > + s->flags &= ~SLAB_FAILSLAB; > + if (buf[0] == '1') > + s->flags |= SLAB_FAILSLAB; Could we at least use a temporary variable to set up the final value and then do a WRITE_ONCE() to s->flags, so the compiler is not allowed to do some funky stuff? Assuming this is really the only place where we modify s->flags during runtime, so we can't miss other updates due to RMW. > + return length; > +} > +SLAB_ATTR(failslab); > #endif > > static ssize_t shrink_show(struct kmem_cache *s, char *buf) > > base-commit: 80e78fcce86de0288793a0ef0f6acf37656ee4cf