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[70.31.27.79]) by smtp.gmail.com with ESMTPSA id bk30-20020a05620a1a1e00b006eeaf9160d6sm4644656qkb.24.2022.10.26.14.42.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Oct 2022 14:42:52 -0700 (PDT) Date: Wed, 26 Oct 2022 17:42:24 -0400 From: Peter Xu To: Mike Kravetz Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Naoya Horiguchi , David Hildenbrand , Axel Rasmussen , Mina Almasry , Rik van Riel , Vlastimil Babka , Matthew Wilcox , Andrew Morton , Wei Chen , stable@vger.kernel.org Subject: Re: [PATCH v2] hugetlb: don't delete vma_lock in hugetlb MADV_DONTNEED processing Message-ID: References: <20221023025047.470646-1-mike.kravetz@oracle.com> MIME-Version: 1.0 In-Reply-To: <20221023025047.470646-1-mike.kravetz@oracle.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666820675; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=FGEAcGAjAMPOazJHa2zAyqoTgNuI6YN3F8egocsHkTg=; b=rxxn7DP0RvTMEzRfS0mfG9oCu9UYr8+PTFsX/AGVnMN7L8LikG0B4kWmVInItRU4pG+vVh dn5+zygUdMXTu1TfV/saNKLhyhfG8us/OOwD9ZmGwhK/JtqOrjQ+ANbAH0egIgGI3r/bKw qDl/1JIZ+bm3vjMhWYY1evtDcbd4XkU= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=R7smR0uq; spf=pass (imf30.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666820675; a=rsa-sha256; cv=none; b=bMgHjVdB5nxBwlV5iJoPYCXHdGZfUMMeB0xGXdqlF8qZKpu+hakhBqg6D7LnCfWVXo4voY PyHAd3ojoXltQH0JA25fwJCTEp8++q+s75CmWqVhbzTsBrGXi1Hmkh/B7SRamzvlbrjWkS RSbZNuA01ESkY9xRpw29UZ4ZOFbPPns= X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: B78A380006 X-Rspam-User: Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=R7smR0uq; spf=pass (imf30.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: 3gnaxxy3cdsb9j4q69kci3gwdqhaqf33 X-HE-Tag: 1666820675-999617 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: Hi, Mike, On Sat, Oct 22, 2022 at 07:50:47PM -0700, Mike Kravetz wrote: [...] > -void __unmap_hugepage_range_final(struct mmu_gather *tlb, > +static void __unmap_hugepage_range_locking(struct mmu_gather *tlb, > struct vm_area_struct *vma, unsigned long start, > unsigned long end, struct page *ref_page, > - zap_flags_t zap_flags) > + zap_flags_t zap_flags, bool final) > { > hugetlb_vma_lock_write(vma); > i_mmap_lock_write(vma->vm_file->f_mapping); > > __unmap_hugepage_range(tlb, vma, start, end, ref_page, zap_flags); > > - /* > - * Unlock and free the vma lock before releasing i_mmap_rwsem. When > - * the vma_lock is freed, this makes the vma ineligible for pmd > - * sharing. And, i_mmap_rwsem is required to set up pmd sharing. > - * This is important as page tables for this unmapped range will > - * be asynchrously deleted. If the page tables are shared, there > - * will be issues when accessed by someone else. > - */ > - __hugetlb_vma_unlock_write_free(vma); > + if (final) { > + /* > + * Unlock and free the vma lock before releasing i_mmap_rwsem. > + * When the vma_lock is freed, this makes the vma ineligible > + * for pmd sharing. And, i_mmap_rwsem is required to set up > + * pmd sharing. This is important as page tables for this > + * unmapped range will be asynchrously deleted. If the page > + * tables are shared, there will be issues when accessed by > + * someone else. > + */ > + __hugetlb_vma_unlock_write_free(vma); > + i_mmap_unlock_write(vma->vm_file->f_mapping); Pure question: can we rely on hugetlb_vm_op_close() to destroy the hugetlb vma lock? I read the comment above, it seems we are trying to avoid racing with pmd sharing, but I don't see how that could ever happen, since iiuc there should only be two places that unmaps the vma (final==true): (1) munmap: we're holding write lock, so no page fault possible (2) exit_mmap: we've already reset current->mm so no page fault possible > + } else { > + i_mmap_unlock_write(vma->vm_file->f_mapping); > + hugetlb_vma_unlock_write(vma); > + } > +} > > - i_mmap_unlock_write(vma->vm_file->f_mapping); > +void __unmap_hugepage_range_final(struct mmu_gather *tlb, > + struct vm_area_struct *vma, unsigned long start, > + unsigned long end, struct page *ref_page, > + zap_flags_t zap_flags) > +{ > + __unmap_hugepage_range_locking(tlb, vma, start, end, ref_page, > + zap_flags, true); > } > > +#ifdef CONFIG_ADVISE_SYSCALLS > +/* > + * Similar setup as in zap_page_range(). madvise(MADV_DONTNEED) can not call > + * zap_page_range for hugetlb vmas as __unmap_hugepage_range_final will delete > + * the associated vma_lock. > + */ > +void clear_hugetlb_page_range(struct vm_area_struct *vma, unsigned long start, > + unsigned long end) > +{ > + struct mmu_notifier_range range; > + struct mmu_gather tlb; > + > + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm, > + start, end); Is mmu_notifier_invalidate_range_start() missing here? > + tlb_gather_mmu(&tlb, vma->vm_mm); > + update_hiwater_rss(vma->vm_mm); > + > + __unmap_hugepage_range_locking(&tlb, vma, start, end, NULL, 0, false); > + > + mmu_notifier_invalidate_range_end(&range); > + tlb_finish_mmu(&tlb); > +} > +#endif > + > void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start, > unsigned long end, struct page *ref_page, > zap_flags_t zap_flags) > diff --git a/mm/madvise.c b/mm/madvise.c > index 2baa93ca2310..90577a669635 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -790,7 +790,10 @@ static int madvise_free_single_vma(struct vm_area_struct *vma, > static long madvise_dontneed_single_vma(struct vm_area_struct *vma, > unsigned long start, unsigned long end) > { > - zap_page_range(vma, start, end - start); > + if (!is_vm_hugetlb_page(vma)) > + zap_page_range(vma, start, end - start); > + else > + clear_hugetlb_page_range(vma, start, end); > return 0; > } This does look a bit unfortunate - zap_page_range() contains yet another is_vm_hugetlb_page() check (further down in unmap_single_vma), it can be very confusing on which code path is really handling hugetlb. The other mm_users check in v3 doesn't need this change, but was a bit hackish to me, because IIUC we're clear on the call paths to trigger this (unmap_vmas), so it seems clean to me to pass that info from the upper stack. Maybe we can have a new zap_flags passed into unmap_single_vma() showing that it's destroying the vma? Thanks, -- Peter Xu