From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 1211D47DF9C for ; Tue, 14 Jul 2026 15:22:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784042524; cv=none; b=Krzd/uzBtTiyCHUbHyswJnEHlvlEtCzsOrk2n+ycr9xfbq/S5leL9CTniDPhkmwq8YRxOnscOwXmkO9Sdb4dfnImMQb5ZSevvXhrqBK+m12ukU+gWHxfusumN93IsShgKkmchBVDbdelZA2nf0Bzj+NUW7pnO/UBXNcx6mZUbnA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784042524; c=relaxed/simple; bh=M1fBj4XuUfX+Y62X0skZM30WSY997q6taqbh6t7yJ3c=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=FuVwFpA1a7r9zK7esms3DuRuFdPnvF0o8ACZSo0kMx/R4PKCjFXL9X6fhUiw9II45iJhZcvEZ6g+bucTR6lRvh6oA7LKDL6jb8iRU+HSTRwfGkPwWv7e8V1W/woiCU6OYJFqGiuzgyDGlNNYuEwBOoqOkmE3IRtuidoYqIvS6I0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CANWhE/+; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="CANWhE/+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF35E1F000E9; Tue, 14 Jul 2026 15:21:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784042522; bh=BCZ3Zd/UYddpYvSXSqBQQiGs1H+xK0sUqICRnDON//8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=CANWhE/+CYS1FfUfjhITGX12OQ6kXuBnyec7afH9+c1HCQzcMYWlRc+wRLQApFBm7 unpSwxn2cqQC7+CQuxuxl2RdNFDAcen4a15J/XZAiipoB3Gp/ih8mMAoTHm0Q0zIdo hisrSw/kpAmgG8mC6yZWDcGZvDIpqAzMVM+SJT8tX8frxA5nKb0Ou4yLgnOfisVO7q n3PfiKP2hme6ksz8x8Rpmdskkf2CPQQeLdHtaVZWc+hbVyt2twbwUCB2X+LwMAPVs8 n/wgXNKWdpA6g3cbHY3wa9b60Y9vId0S1GdtplZG5kdaz/qX7UYQKFrl12Di7yyYS1 FTgpuHUmHLh7Q== Message-ID: Date: Tue, 14 Jul 2026 17:21:57 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH slab/for-next-fixes v3 4/4] mm/slab: prevent unbounded recursion in free path with new kmalloc type Content-Language: en-US To: "Harry Yoo (Oracle)" , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , "Liam R. Howlett" , Suren Baghdasaryan , Hao Ge , Kees Cook , Pedro Falcato , Shakeel Butt , Danielle Constantino Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260713-kmalloc-no-objext-v3-0-47c7bd138de7@kernel.org> <20260713-kmalloc-no-objext-v3-4-47c7bd138de7@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20260713-kmalloc-no-objext-v3-4-47c7bd138de7@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/13/26 16:28, Harry Yoo (Oracle) wrote: > @@ -2168,14 +2132,20 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, > unsigned long new_exts; > unsigned long old_exts; > struct slabobj_ext *vec; > - size_t sz; > + size_t sz = sizeof(struct slabobj_ext) * slab->objects; > > gfp &= ~OBJCGS_CLEAR_MASK; > - /* Prevent recursive extension vector allocation */ > - alloc_flags |= SLAB_ALLOC_NO_RECURSE; > - alloc_flags &= ~SLAB_ALLOC_NEW_SLAB; > + /* > + * In most cases, obj_exts arrays are allocated from normal kmalloc. > + * However, normal kmalloc caches must allocate them from > + * KMALLOC_NO_OBJ_EXT caches to prevent recursion. > + */ > + if (is_kmalloc_normal(s)) { > + VM_WARN_ON_ONCE(!need_kmalloc_no_objext()); As discussed off-list, this can false positively trigger due to a race with shutdown_mem_profiling() so I'll remove it. > + alloc_flags |= SLAB_ALLOC_NO_OBJ_EXT; > + } > > - sz = obj_exts_alloc_size(s, slab, gfp); > + alloc_flags &= ~SLAB_ALLOC_NEW_SLAB; > > /* This will use kmalloc_nolock() if alloc_flags say so */ > vec = kmalloc_flags(sz, gfp | __GFP_ZERO, alloc_flags, slab_nid(slab));