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[35.77.58.189]) by smtp.gmail.com with ESMTPSA id z4-20020a170902ccc400b001677fa34a07sm3693091ple.43.2022.07.13.02.26.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Jul 2022 02:26:04 -0700 (PDT) Date: Wed, 13 Jul 2022 09:25:59 +0000 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Christoph Lameter Cc: Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Roman Gushchin , Joe Perches , Vasily Averin , Matthew WilCox , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Marco Elver Subject: Re: [PATCH 16/16] mm/sl[au]b: check if large object is valid in __ksize() Message-ID: References: <20220712133946.307181-1-42.hyeyoo@gmail.com> <20220712133946.307181-17-42.hyeyoo@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1657704366; a=rsa-sha256; cv=none; b=wrkBi87SlOl+PXWBWl8DrC4ZBDdFSoacZtD5gHE/9XIwF7lOwWIB1tC0C2ikShHp8BKdDW PFwkbjmF7aTfzrewsnZuw8SFJMbynm8IvMdsAO1IEJVUdzbhQ676LxOtoORW1iWiegfLlx FEbeYavzN7cRlAsA5kUBoAEjxKpckfY= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=JUlmieSV; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf28.hostedemail.com: domain of 42.hyeyoo@gmail.com designates 209.85.216.54 as permitted sender) smtp.mailfrom=42.hyeyoo@gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1657704366; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=vQEG1g5aM3Tjy/jRcXsLvnY4WNvgT+rmdCcMcFykq/0=; b=ZWaQUNcDpsaz6L1ng9r8QqaUyIHONNDx1CAvqy/fvKl1Z1SMP3i3QTJNyIBRL7QOd8RVDz 9CaDW9UVpHE1JTiGIGbsIo6bscPXT+fXX5PxzyimNEgPUBtoKjqxU6J2JmkIVIDADqx24q ldIJsRrjMuktUbNdda8DJ2RKwPRqe30= X-Rspam-User: X-Stat-Signature: w3khae7bnx5qm98q6ish74qrrupcay1q X-Rspamd-Queue-Id: 7415DC0079 Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=JUlmieSV; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf28.hostedemail.com: domain of 42.hyeyoo@gmail.com designates 209.85.216.54 as permitted sender) smtp.mailfrom=42.hyeyoo@gmail.com X-Rspamd-Server: rspam03 X-HE-Tag: 1657704366-436214 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 Tue, Jul 12, 2022 at 05:13:44PM +0200, Christoph Lameter wrote: > On Tue, 12 Jul 2022, Hyeonggon Yoo wrote: > > > __ksize() returns size of objects allocated from slab allocator. > > When invalid object is passed to __ksize(), returning zero > > prevents further memory corruption and makes caller be able to > > check if there is an error. > > > > If address of large object is not beginning of folio or size of > > the folio is too small, it must be invalid. Return zero in such cases. > > Why return 0 if there is an error and why bother the callers with these > checks. BUG()? I thought BUG should be used when there is no other solution. > > diff --git a/mm/slab_common.c b/mm/slab_common.c > > index 1f8db7959366..0d6cbe9d7ad0 100644 > > --- a/mm/slab_common.c > > +++ b/mm/slab_common.c > > @@ -1013,8 +1013,12 @@ size_t __ksize(const void *object) > > > > folio = virt_to_folio(object); > > > > - if (unlikely(!folio_test_slab(folio))) > > + if (unlikely(!folio_test_slab(folio))) { > > + if (WARN_ON(object != folio_address(folio) || > > + folio_size(folio) <= KMALLOC_MAX_CACHE_SIZE)) > > Hmmm... This may change things a bit. Before this patch it was possible to > determine the storage size of order-0 pages using ksize(). Now this > returns 0? > > I guess this is an error since the order-0 page cannot come from slab > allocations. comment in ksize() says: "The caller must guarantee that objp points to a valid object previously allocated with either kmalloc() or kmem_cache_alloc()." It should not be used on order-0 page that is not allocated from slab. No?