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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> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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-Spam-Level: X-Rspamd-Queue-Id: E528022015 X-Spam-Score: -1.51 X-Spam-Flag: NO X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [-1.51 / 50.00]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCVD_TLS_ALL(0.00)[]; RCPT_COUNT_SEVEN(0.00)[10]; FUZZY_BLOCKED(0.00)[rspamd.com]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; MISSING_XM_UA(0.00)[]; DWL_DNSWL_BLOCKED(0.00)[suse.de:dkim]; FREEMAIL_ENVRCPT(0.00)[126.com,gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[126.com,linux-foundation.org,kvack.org,vger.kernel.org,gmail.com,redhat.com,linux.alibaba.com,hygon.cn]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:106:10:150:64:167:received,2a07:de40:b281:104:10:150:64:97:from]; DKIM_TRACE(0.00)[suse.de:+] 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