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Thu, 22 May 2025 05:34:55 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id UOFnKX+3LmgvbQAAD6G6ig (envelope-from ); Thu, 22 May 2025 05:34:55 +0000 Date: Thu, 22 May 2025 07:34:54 +0200 From: Oscar Salvador To: Muchun Song Cc: yangge1116@126.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, 21cnbao@gmail.com, david@redhat.com, baolin.wang@linux.alibaba.com, liuzixing@hygon.cn Subject: Re: [PATCH] mm/hugetlb: fix kernel NULL pointer dereference when replacing free hugetlb folios Message-ID: References: <1747884137-26685-1-git-send-email-yangge1116@126.com> <644FF836-9DC7-42B4-BACE-C433E637B885@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <644FF836-9DC7-42B4-BACE-C433E637B885@linux.dev> X-Rspamd-Action: no action X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: BBE9C20003 X-Stat-Signature: sz8qw3xwmcimnqbuqhugi5yocwzakmop X-Rspam-User: X-HE-Tag: 1747892097-638528 X-HE-Meta: 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 3O7z0aPu fpUG/Lj69PBhTcmpuWLu/UspEOSNvoXp/OkQxXPcReqIfzDL1Q+rzgUuqUq6DnbcEoZ+d1usEPd9MziCBTklqoAb9gx0tzI0IspOHpwxQr7mDlvpUTEUvMhlvmMtPvRWMeUGyQz8hfgVN1CAs2ZSAaTUjTCxiKrialz2AbxYBgPd00LhXndLoUV2tKDaLRPUbHTDgyB3P0r71MpvWUHTEx4lMLFgIiBm1pRaSAsKrvysAjCXFwo9PBrK1ToOr1fBkinqRQtBQA1Ec8Fg= 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: List-Subscribe: List-Unsubscribe: On Thu, May 22, 2025 at 11:47:05AM +0800, Muchun Song wrote: > Thanks for fixing this problem. BTW, in order to catch future similar problem, > it is better to add WARN_ON into folio_hstate() to assert if hugetlb_lock > is not held when folio's reference count is zero. For this fix, LGTM. Why cannot we put all the burden in alloc_and_dissolve_hugetlb_folio(), which will again check things under the lock? I mean, I would be ok to save cycles and check upfront in replace_free_hugepage_folios(), but the latter has only one user which is alloc_contig_range(), which is not really an expected-to-be optimized function. diff --git a/mm/hugetlb.c b/mm/hugetlb.c index bd8971388236..b4d937732256 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2924,13 +2924,6 @@ int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) while (start_pfn < end_pfn) { folio = pfn_folio(start_pfn); - if (folio_test_hugetlb(folio)) { - h = folio_hstate(folio); - } else { - start_pfn++; - continue; - } - if (!folio_ref_count(folio)) { ret = alloc_and_dissolve_hugetlb_folio(h, folio, &isolate_list); -- Oscar Salvador SUSE Labs