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b=aXtznABHufngIYSDtYdd01SpLEVfLER3WrVjAondkKqurHFL/zI/WCeIWW6NSri5Z H1a1ejxqy6k+D1ez67uV9a2ksETHTzdUaomcq7TPd+QKL477M0+e+EFQrVCQOFgRay m/PaoBsedbdvh92ZeQGsXNMn1WlQoqocJ+xh31wY= Date: Fri, 22 Aug 2025 18:07:08 -0700 From: Andrew Morton To: Jeongjun Park Cc: muchun.song@linux.dev, osalvador@suse.de, david@redhat.com, leitao@debian.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+417aeb05fd190f3a6da9@syzkaller.appspotmail.com Subject: Re: [PATCH] mm/hugetlb: add missing hugetlb_lock in __unmap_hugepage_range() Message-Id: <20250822180708.86e79941d7e47e3bb759b193@linux-foundation.org> In-Reply-To: <20250822055857.1142454-1-aha310510@gmail.com> References: <20250822055857.1142454-1-aha310510@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: D68BC140005 X-Stat-Signature: mcu79dgomw9q4xbo6h6ncgmdzo4biq71 X-Rspam-User: X-HE-Tag: 1755911230-152393 X-HE-Meta: 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 yPpffDpF N67cq8rhv1xJgfA0UxdkyRzcajP4RPKM3IACTnNP3JLf6oEy+rTYDWmn6s3uXXa/vFWirGpHu2WTFXBjv7vdLw+wNAxBZNUoZQ5Z6U59ZCwA2BP87rlgvwDWLiBcWZIYfAhDP3HhWY0NwH/KsJhpUgF7A7Ctb7b4Gix0a1W9DBWZ8BhJgtvu79ICSrgi+ySsd4vQ23uAy7zNn1NFEbF2voIIlMeew73qquhx/AtLjvC7KQabTRrNQdFzb4+zraB9cA+Re2Sp+QEkaJwZ875M86URQ/nee9k2UUdDp2hgy1SXkPGUnRZcxCgMcfBVJDXDpSXdwmzcUkxHboavJgzx52O/Fa9afGj2jfVE3Q2yltQ6+/fErDbz5vSnjVMxYnROID1f2frFqMCd7E3O7huiCjFp6x1ooRKOMTn26SxrrFcqxvB4HDcyDSV88yLqG81r5QGRF 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 Fri, 22 Aug 2025 14:58:57 +0900 Jeongjun Park wrote: > When restoring a reservation for an anonymous page, we need to check to > freeing a surplus. However, __unmap_hugepage_range() causes data race > because it reads h->surplus_huge_pages without the protection of > hugetlb_lock. > > Therefore, we need to add missing hugetlb_lock. > > ... > > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5951,6 +5951,8 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, > * If there we are freeing a surplus, do not set the restore > * reservation bit. > */ > + spin_lock_irq(&hugetlb_lock); > + > if (!h->surplus_huge_pages && __vma_private_lock(vma) && > folio_test_anon(folio)) { > folio_set_hugetlb_restore_reserve(folio); > @@ -5958,6 +5960,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, > adjust_reservation = true; > } > > + spin_unlock_irq(&hugetlb_lock); > spin_unlock(ptl); > Does hugetlb_lock nest inside page_table_lock? It's a bit sad to be taking a global lock just to defend against some alleged data race which probably never happens. Doing it once per hugepage probably won't matter but still, is there something more proportionate that we can do here?