From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id A47A128028E for ; Tue, 27 Sep 2016 12:08:50 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id b130so12656442wmc.2 for ; Tue, 27 Sep 2016 09:08:50 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id n64si14449964wmn.41.2016.09.27.09.08.34 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 27 Sep 2016 09:08:34 -0700 (PDT) From: Jan Kara Subject: [PATCH 16/20] mm: Provide helper for finishing mkwrite faults Date: Tue, 27 Sep 2016 18:08:20 +0200 Message-Id: <1474992504-20133-17-git-send-email-jack@suse.cz> In-Reply-To: <1474992504-20133-1-git-send-email-jack@suse.cz> References: <1474992504-20133-1-git-send-email-jack@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org Cc: linux-fsdevel@vger.kernel.org, linux-nvdimm@lists.01.org, Dan Williams , Ross Zwisler , "Kirill A. Shutemov" , Jan Kara Provide a helper function for finishing write faults due to PTE being read-only. The helper will be used by DAX to avoid the need of complicating generic MM code with DAX locking specifics. Signed-off-by: Jan Kara --- include/linux/mm.h | 1 + mm/memory.c | 65 +++++++++++++++++++++++++++++++----------------------- 2 files changed, 39 insertions(+), 27 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 1055f2ece80d..e5a014be8932 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -617,6 +617,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) int alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg, struct page *page); int finish_fault(struct vm_fault *vmf); +int finish_mkwrite_fault(struct vm_fault *vmf); #endif /* diff --git a/mm/memory.c b/mm/memory.c index f49e736d6a36..8c8cb7f2133e 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2266,6 +2266,36 @@ oom: return VM_FAULT_OOM; } +/** + * finish_mkrite_fault - finish page fault making PTE writeable once the page + * page is prepared + * + * @vmf: structure describing the fault + * + * This function handles all that is needed to finish a write page fault due + * to PTE being read-only once the mapped page is prepared. It handles locking + * of PTE and modifying it. The function returns VM_FAULT_WRITE on success, + * 0 when PTE got changed before we acquired PTE lock. + * + * The function expects the page to be locked or other protection against + * concurrent faults / writeback (such as DAX radix tree locks). + */ +int finish_mkwrite_fault(struct vm_fault *vmf) +{ + vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, vmf->address, + &vmf->ptl); + /* + * We might have raced with another page fault while we released the + * pte_offset_map_lock. + */ + if (!pte_same(*vmf->pte, vmf->orig_pte)) { + pte_unmap_unlock(vmf->pte, vmf->ptl); + return 0; + } + wp_page_reuse(vmf); + return VM_FAULT_WRITE; +} + /* * Handle write page faults for VM_MIXEDMAP or VM_PFNMAP for a VM_SHARED * mapping @@ -2282,16 +2312,7 @@ static int wp_pfn_shared(struct vm_fault *vmf) ret = vma->vm_ops->pfn_mkwrite(vma, vmf); if (ret & VM_FAULT_ERROR) return ret; - vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, - vmf->address, &vmf->ptl); - /* - * We might have raced with another page fault while we - * released the pte_offset_map_lock. - */ - if (!pte_same(*vmf->pte, vmf->orig_pte)) { - pte_unmap_unlock(vmf->pte, vmf->ptl); - return 0; - } + return finish_mkwrite_fault(vmf); } wp_page_reuse(vmf); return VM_FAULT_WRITE; @@ -2301,7 +2322,6 @@ static int wp_page_shared(struct vm_fault *vmf) __releases(vmf->ptl) { struct vm_area_struct *vma = vmf->vma; - int page_mkwrite = 0; get_page(vmf->page); @@ -2315,26 +2335,17 @@ static int wp_page_shared(struct vm_fault *vmf) put_page(vmf->page); return tmp; } - /* - * Since we dropped the lock we need to revalidate - * the PTE as someone else may have changed it. If - * they did, we just return, as we can count on the - * MMU to tell us if they didn't also make it writable. - */ - vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, - vmf->address, &vmf->ptl); - if (!pte_same(*vmf->pte, vmf->orig_pte)) { + tmp = finish_mkwrite_fault(vmf); + if (unlikely(!tmp || (tmp & + (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) { unlock_page(vmf->page); - pte_unmap_unlock(vmf->pte, vmf->ptl); put_page(vmf->page); - return 0; + return tmp; } - page_mkwrite = 1; - } - - wp_page_reuse(vmf); - if (!page_mkwrite) + } else { + wp_page_reuse(vmf); lock_page(vmf->page); + } fault_dirty_shared_page(vma, vmf->page); put_page(vmf->page); -- 2.6.6 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org