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Wed, 31 Jul 2024 15:08:26 +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 q007AGpTqmayAQAAD6G6ig (envelope-from ); Wed, 31 Jul 2024 15:08:26 +0000 Date: Wed, 31 Jul 2024 17:08:24 +0200 From: Oscar Salvador To: Lorenzo Stoakes Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Peter Xu , Muchun Song , David Hildenbrand , Donet Tom , Matthew Wilcox , Vlastimil Babka , Michal Hocko Subject: Re: [PATCH v2 6/9] mm: Make hugetlb mappings go through mm_get_unmapped_area_vmflags Message-ID: References: <20240729091018.2152-1-osalvador@suse.de> <20240729091018.2152-7-osalvador@suse.de> <8a57e184-4994-4642-959d-44dc7efbceca@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8a57e184-4994-4642-959d-44dc7efbceca@lucifer.local> X-Rspamd-Action: no action X-Rspam-User: X-Stat-Signature: m93i4uzbrs6o5hr3yrkh85tred74msso X-Rspamd-Queue-Id: 8682B40024 X-Rspamd-Server: rspam11 X-HE-Tag: 1722438508-304520 X-HE-Meta: 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 Ofmgpk8/ J4I2NaQURyX8X1vN3M7lM/FNEIP/uP6Dk6yoz40GZgkU3xESRbSJMqchHJhA5fw23uL8GWJ887+kgz3fQDmfgiM+jZrEllTI5PCFCNqq8+SwD8W+xkKZ1MgEvKTU6jm+JVnrQ/IyY239lsIag3I4XD37oyB1PqBUEmkYVvJFLpWYis0x0aeHywThculDWUdcvMkpOsHaCZaUoFAJq7BCpLYTUohCgjDYu8a9jZXKGve4/g7F6l8Ep4pnsN0YhOmyF8L4FZqMNUcx4OpAPz874xdZT+Cr6nMFtza4894PLlSfjjIfrWDbePSaVHw== 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 Wed, Jul 31, 2024 at 12:02:47PM +0100, Lorenzo Stoakes wrote: > On Mon, Jul 29, 2024 at 11:10:15AM GMT, Oscar Salvador wrote: > > * Someone wants to read @bytes from a HWPOISON hugetlb @page from @offset. > > @@ -1300,7 +1307,6 @@ static const struct file_operations hugetlbfs_file_operations = { > > .read_iter = hugetlbfs_read_iter, > > .mmap = hugetlbfs_file_mmap, > > .fsync = noop_fsync, > > - .get_unmapped_area = hugetlb_get_unmapped_area, > > This is causing a NULL pointer deref error in the mm self-tests, > specifically hugepage-shm. > > This is because in __get_unmapped_area(), you check to see if the file has > an f_ops->get_unampped_area() however ('wonderfully'...) the shm stuff > wraps it, so this will be shm_get_unmapped_area() which then accesses the > underlying hugetlb file and _unconditionally_ calls > f_op->get_unmapped_area(), which you just made NULL and... kaboom :) > > You can't even add null check in to this wrapper as at this point > everything assumes that you _can_ get an unmapped area. So yeah, it's kinda > broken. > > This makes me think the whole thing is super-delicate and you probably need > to rethink this approach carefully, or least _very carefully_ audit users > of this operation. Thanks for reporting this Lorenzo, highly appreciated. I will check, but.. > By doing this you are causing an compilation error (at least on my compiler > with an x86-64 defconfig-based build): > > arch/x86/mm/hugetlbpage.c:84:1: error: no previous prototype for > ‘hugetlb_get_unmapped_area’ [-Werror=missing-prototypes] > 84 | hugetlb_get_unmapped_area(struct file *file, unsigned long addr, > | ^~~~~~~~~~~~~~~~~~~~~~~~~ Something is off here. git grep hugetlb_get_unmapped_area returns nothing. After this, arch/x86/mm/hugetlbpage.c should only contain: #ifdef CONFIG_X86_64 bool __init arch_hugetlb_valid_size(unsigned long size) { if (size == PMD_SIZE) return true; else if (size == PUD_SIZE && boot_cpu_has(X86_FEATURE_GBPAGES)) return true; else return false; } #ifdef CONFIG_CONTIG_ALLOC static __init int gigantic_pages_init(void) { /* With compaction or CMA we can allocate gigantic pages at runtime */ if (boot_cpu_has(X86_FEATURE_GBPAGES)) hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT); return 0; } arch_initcall(gigantic_pages_init); #endif #endif so what is going here? Maybe the series was not properly applied to mm-unstable? I will have a look. -- Oscar Salvador SUSE Labs