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[141.146.126.79]) by mx.google.com with ESMTPS id p18si108265ioh.40.2018.12.22.14.30.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 22 Dec 2018 14:30:42 -0800 (PST) Received-SPF: pass (google.com: domain of mike.kravetz@oracle.com designates 141.146.126.79 as permitted sender) client-ip=141.146.126.79; Authentication-Results: mx.google.com; dkim=pass header.i=@oracle.com header.s=corp-2018-07-02 header.b=TaQV2uOx; spf=pass (google.com: domain of mike.kravetz@oracle.com designates 141.146.126.79 as permitted sender) smtp.mailfrom=mike.kravetz@oracle.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=oracle.com Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.22/8.16.0.22) with SMTP id wBMMTGki066199; Sat, 22 Dec 2018 22:30:34 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references; s=corp-2018-07-02; bh=tbthBz9kkb1Ac0hzw6ThNSAvFupxeJ/Q4TNxE0uQxXo=; b=TaQV2uOxCvhI8IuB4k0g875QI1DSu0aecYn1pwvbBFF53lkQGj3y551gIY+T+njKfX/u 2WeEcRGFGdy9w7t4WPMzDgzjSLpMJJi6ZmTQiQRQgYnag8c6W4eDlffCKSCpi27sDHl7 v1GXS4ZzpiuNWEHX/ZsHVHcDZXrVUkcMmrJYGAYTFgE5LSKSSmhL47KkNomr6EMEfZDk s4z/X1axMkgv6K7HpZT/OvbUwDH5858oMvheZTLLH0PKkVdS9XGnAMmggArrlkHiaFY1 heO4V4AGggmrMz6WerhRBFUcGh5YQuBcgCbGp20B471mc051udpohvvFQJ5Ic3jPLJiX GQ== Received: from aserv0021.oracle.com (aserv0021.oracle.com [141.146.126.233]) by aserp2130.oracle.com with ESMTP id 2phasdhh0k-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sat, 22 Dec 2018 22:30:34 +0000 Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserv0021.oracle.com (8.14.4/8.14.4) with ESMTP id wBMMUYXv021308 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sat, 22 Dec 2018 22:30:34 GMT Received: from abhmp0007.oracle.com (abhmp0007.oracle.com [141.146.116.13]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id wBMMUXWB027674; Sat, 22 Dec 2018 22:30:33 GMT Received: from monkey.oracle.com (/50.38.38.67) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Sat, 22 Dec 2018 14:30:33 -0800 From: Mike Kravetz To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Michal Hocko , Hugh Dickins , Naoya Horiguchi , "Aneesh Kumar K . V" , Andrea Arcangeli , "Kirill A . Shutemov" , Davidlohr Bueso , Prakash Sangappa , Andrew Morton , Mike Kravetz , stable@vger.kernel.org Subject: [PATCH v3 1/2] hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization Date: Sat, 22 Dec 2018 14:30:12 -0800 Message-Id: <20181222223013.22193-2-mike.kravetz@oracle.com> X-Mailer: git-send-email 2.17.2 In-Reply-To: <20181222223013.22193-1-mike.kravetz@oracle.com> References: <20181222223013.22193-1-mike.kravetz@oracle.com> X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9115 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1812220204 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: X-Virus-Scanned: ClamAV using ClamSMTP While looking at BUGs associated with invalid huge page map counts, it was discovered and observed that a huge pte pointer could become 'invalid' and point to another task's page table. Consider the following: A task takes a page fault on a shared hugetlbfs file and calls huge_pte_alloc to get a ptep. Suppose the returned ptep points to a shared pmd. Now, another task truncates the hugetlbfs file. As part of truncation, it unmaps everyone who has the file mapped. If the range being truncated is covered by a shared pmd, huge_pmd_unshare will be called. For all but the last user of the shared pmd, huge_pmd_unshare will clear the pud pointing to the pmd. If the task in the middle of the page fault is not the last user, the ptep returned by huge_pte_alloc now points to another task's page table or worse. This leads to bad things such as incorrect page map/reference counts or invalid memory references. To fix, expand the use of i_mmap_rwsem as follows: - i_mmap_rwsem is held in read mode whenever huge_pmd_share is called. huge_pmd_share is only called via huge_pte_alloc, so callers of huge_pte_alloc take i_mmap_rwsem before calling. In addition, callers of huge_pte_alloc continue to hold the semaphore until finished with the ptep. - i_mmap_rwsem is held in write mode whenever huge_pmd_unshare is called. Cc: Fixes: 39dde65c9940 ("shared page table for hugetlb page") Signed-off-by: Mike Kravetz --- mm/hugetlb.c | 67 ++++++++++++++++++++++++++++++++++----------- mm/memory-failure.c | 14 +++++++++- mm/migrate.c | 13 ++++++++- mm/rmap.c | 4 +++ mm/userfaultfd.c | 11 ++++++-- 5 files changed, 89 insertions(+), 20 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 309fb8c969af..2a3162030167 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3239,6 +3239,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, int cow; struct hstate *h = hstate_vma(vma); unsigned long sz = huge_page_size(h); + struct address_space *mapping = vma->vm_file->f_mapping; unsigned long mmun_start; /* For mmu_notifiers */ unsigned long mmun_end; /* For mmu_notifiers */ int ret = 0; @@ -3247,14 +3248,25 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, mmun_start = vma->vm_start; mmun_end = vma->vm_end; - if (cow) + if (cow) { mmu_notifier_invalidate_range_start(src, mmun_start, mmun_end); + } else { + /* + * For shared mappings i_mmap_rwsem must be held to call + * huge_pte_alloc, otherwise the returned ptep could go + * away if part of a shared pmd and another thread calls + * huge_pmd_unshare. + */ + i_mmap_lock_read(mapping); + } for (addr = vma->vm_start; addr < vma->vm_end; addr += sz) { spinlock_t *src_ptl, *dst_ptl; + src_pte = huge_pte_offset(src, addr, sz); if (!src_pte) continue; + dst_pte = huge_pte_alloc(dst, addr, sz); if (!dst_pte) { ret = -ENOMEM; @@ -3325,6 +3337,8 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, if (cow) mmu_notifier_invalidate_range_end(src, mmun_start, mmun_end); + else + i_mmap_unlock_read(mapping); return ret; } @@ -3772,14 +3786,18 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, }; /* - * hugetlb_fault_mutex must be dropped before - * handling userfault. Reacquire after handling - * fault to make calling code simpler. + * hugetlb_fault_mutex and i_mmap_rwsem must be + * dropped before handling userfault. Reacquire + * after handling fault to make calling code simpler. */ hash = hugetlb_fault_mutex_hash(h, mm, vma, mapping, idx, haddr); mutex_unlock(&hugetlb_fault_mutex_table[hash]); + i_mmap_unlock_read(mapping); + ret = handle_userfault(&vmf, VM_UFFD_MISSING); + + i_mmap_lock_read(mapping); mutex_lock(&hugetlb_fault_mutex_table[hash]); goto out; } @@ -3927,6 +3945,11 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, ptep = huge_pte_offset(mm, haddr, huge_page_size(h)); if (ptep) { + /* + * Since we hold no locks, ptep could be stale. That is + * OK as we are only making decisions based on content and + * not actually modifying content here. + */ entry = huge_ptep_get(ptep); if (unlikely(is_hugetlb_entry_migration(entry))) { migration_entry_wait_huge(vma, mm, ptep); @@ -3934,20 +3957,31 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry))) return VM_FAULT_HWPOISON_LARGE | VM_FAULT_SET_HINDEX(hstate_index(h)); - } else { - ptep = huge_pte_alloc(mm, haddr, huge_page_size(h)); - if (!ptep) - return VM_FAULT_OOM; } + /* + * Acquire i_mmap_rwsem before calling huge_pte_alloc and hold + * until finished with ptep. This prevents huge_pmd_unshare from + * being called elsewhere and making the ptep no longer valid. + * + * ptep could have already be assigned via huge_pte_offset. That + * is OK, as huge_pte_alloc will return the same value unless + * something changed. + */ mapping = vma->vm_file->f_mapping; - idx = vma_hugecache_offset(h, vma, haddr); + i_mmap_lock_read(mapping); + ptep = huge_pte_alloc(mm, haddr, huge_page_size(h)); + if (!ptep) { + i_mmap_unlock_read(mapping); + return VM_FAULT_OOM; + } /* * Serialize hugepage allocation and instantiation, so that we don't * get spurious allocation failures if two CPUs race to instantiate * the same page in the page cache. */ + idx = vma_hugecache_offset(h, vma, haddr); hash = hugetlb_fault_mutex_hash(h, mm, vma, mapping, idx, haddr); mutex_lock(&hugetlb_fault_mutex_table[hash]); @@ -4035,6 +4069,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, } out_mutex: mutex_unlock(&hugetlb_fault_mutex_table[hash]); + i_mmap_unlock_read(mapping); /* * Generally it's safe to hold refcount during waiting page lock. But * here we just wait to defer the next page fault to avoid busy loop and @@ -4639,10 +4674,12 @@ void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, * Search for a shareable pmd page for hugetlb. In any case calls pmd_alloc() * and returns the corresponding pte. While this is not necessary for the * !shared pmd case because we can allocate the pmd later as well, it makes the - * code much cleaner. pmd allocation is essential for the shared case because - * pud has to be populated inside the same i_mmap_rwsem section - otherwise - * racing tasks could either miss the sharing (see huge_pte_offset) or select a - * bad pmd for sharing. + * code much cleaner. + * + * This routine must be called with i_mmap_rwsem held in at least read mode. + * For hugetlbfs, this prevents removal of any page table entries associated + * with the address space. This is important as we are setting up sharing + * based on existing page table entries (mappings). */ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) { @@ -4659,7 +4696,6 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) if (!vma_shareable(vma, addr)) return (pte_t *)pmd_alloc(mm, pud, addr); - i_mmap_lock_write(mapping); vma_interval_tree_foreach(svma, &mapping->i_mmap, idx, idx) { if (svma == vma) continue; @@ -4689,7 +4725,6 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) spin_unlock(ptl); out: pte = (pte_t *)pmd_alloc(mm, pud, addr); - i_mmap_unlock_write(mapping); return pte; } @@ -4700,7 +4735,7 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) * indicated by page_count > 1, unmap is achieved by clearing pud and * decrementing the ref count. If count == 1, the pte page is not shared. * - * called with page table lock held. + * Called with page table lock held and i_mmap_rwsem held in write mode. * * returns: 1 successfully unmapped a shared pte page * 0 the underlying pte page is not shared, or it is the last user diff --git a/mm/memory-failure.c b/mm/memory-failure.c index 0cd3de3550f0..b992d1295578 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1028,7 +1028,19 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn, if (kill) collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED); - unmap_success = try_to_unmap(hpage, ttu); + if (!PageHuge(hpage)) { + unmap_success = try_to_unmap(hpage, ttu); + } else { + /* + * For hugetlb pages, try_to_unmap could potentially call + * huge_pmd_unshare. Because of this, take semaphore in + * write mode here and set TTU_RMAP_LOCKED to indicate we + * have taken the lock at this higer level. + */ + i_mmap_lock_write(mapping); + unmap_success = try_to_unmap(hpage, ttu|TTU_RMAP_LOCKED); + i_mmap_unlock_write(mapping); + } if (!unmap_success) pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n", pfn, page_mapcount(hpage)); diff --git a/mm/migrate.c b/mm/migrate.c index 84381b55b2bd..725edaef238a 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1307,8 +1307,19 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, goto put_anon; if (page_mapped(hpage)) { + struct address_space *mapping = page_mapping(hpage); + + /* + * try_to_unmap could potentially call huge_pmd_unshare. + * Because of this, take semaphore in write mode here and + * set TTU_RMAP_LOCKED to let lower levels know we have + * taken the lock. + */ + i_mmap_lock_write(mapping); try_to_unmap(hpage, - TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS); + TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS| + TTU_RMAP_LOCKED); + i_mmap_unlock_write(mapping); page_was_mapped = 1; } diff --git a/mm/rmap.c b/mm/rmap.c index 85b7f9423352..c566bd552535 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -25,6 +25,7 @@ * page->flags PG_locked (lock_page) * hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share) * mapping->i_mmap_rwsem + * hugetlb_fault_mutex (hugetlbfs specific page fault mutex) * anon_vma->rwsem * mm->page_table_lock or pte_lock * zone_lru_lock (in mark_page_accessed, isolate_lru_page) @@ -1374,6 +1375,9 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, /* * If sharing is possible, start and end will be adjusted * accordingly. + * + * If called for a huge page, caller must hold i_mmap_rwsem + * in write mode as it is possible to call huge_pmd_unshare. */ adjust_range_if_pmd_sharing_possible(vma, &start, &end); } diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 458acda96f20..48368589f519 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -267,10 +267,14 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, VM_BUG_ON(dst_addr & ~huge_page_mask(h)); /* - * Serialize via hugetlb_fault_mutex + * Serialize via i_mmap_rwsem and hugetlb_fault_mutex. + * i_mmap_rwsem ensures the dst_pte remains valid even + * in the case of shared pmds. fault mutex prevents + * races with other faulting threads. */ - idx = linear_page_index(dst_vma, dst_addr); mapping = dst_vma->vm_file->f_mapping; + i_mmap_lock_read(mapping); + idx = linear_page_index(dst_vma, dst_addr); hash = hugetlb_fault_mutex_hash(h, dst_mm, dst_vma, mapping, idx, dst_addr); mutex_lock(&hugetlb_fault_mutex_table[hash]); @@ -279,6 +283,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, dst_pte = huge_pte_alloc(dst_mm, dst_addr, huge_page_size(h)); if (!dst_pte) { mutex_unlock(&hugetlb_fault_mutex_table[hash]); + i_mmap_unlock_read(mapping); goto out_unlock; } @@ -286,6 +291,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, dst_pteval = huge_ptep_get(dst_pte); if (!huge_pte_none(dst_pteval)) { mutex_unlock(&hugetlb_fault_mutex_table[hash]); + i_mmap_unlock_read(mapping); goto out_unlock; } @@ -293,6 +299,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, dst_addr, src_addr, &page); mutex_unlock(&hugetlb_fault_mutex_table[hash]); + i_mmap_unlock_read(mapping); vm_alloc_shared = vm_shared; cond_resched(); From patchwork Sat Dec 22 22:30:13 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mike Kravetz X-Patchwork-Id: 10741527 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 053766C5 for ; Sat, 22 Dec 2018 22:30:52 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id E82CB28A5D for ; Sat, 22 Dec 2018 22:30:51 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id DC7F128A60; Sat, 22 Dec 2018 22:30:51 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_NONE, UNPARSEABLE_RELAY autolearn=ham version=3.3.1 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8B51828A5D for ; 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[141.146.126.79]) by mx.google.com with ESMTPS id b21si7593350itc.73.2018.12.22.14.30.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 22 Dec 2018 14:30:44 -0800 (PST) Received-SPF: pass (google.com: domain of mike.kravetz@oracle.com designates 141.146.126.79 as permitted sender) client-ip=141.146.126.79; Authentication-Results: mx.google.com; dkim=pass header.i=@oracle.com header.s=corp-2018-07-02 header.b=cawiLHyv; spf=pass (google.com: domain of mike.kravetz@oracle.com designates 141.146.126.79 as permitted sender) smtp.mailfrom=mike.kravetz@oracle.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=oracle.com Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.22/8.16.0.22) with SMTP id wBMMTqYX066326; Sat, 22 Dec 2018 22:30:37 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references; s=corp-2018-07-02; bh=VKohsUrMKKgNGnQ0gYAjxcXhQ+gP8dLYA/uers/DyHM=; b=cawiLHyvjX8YZrNblKRgGF2vBdj3B//f2HVRxrhsu+XtAz5UM2lbR8HXrLiY9/BaZb2a 2n9L02+IHeEE+rezbMDJE/xNfPrXGNdmeFArjT7OCDph0ZoPBLjyKIuU4mTwqjaiJof6 xIs3kVf4ZEUaedyCPoe2hQJYSLEuCvVKOCxcz5jINxTt8oEHXfwdpD2hk/jNM4qTxsDE pg1TJUb4qffz9hfjapPG7E/aLoIkiJR5XLnESiH9aRHxpS+FJWPIkEjnllkU72IrfgU+ Ri7n4LDOcVk6jNhAOs49zCgTR80spaf2n4msAzmxM+0lQwhcUIei1zk+U7gbXjfQKg/W lA== Received: from aserv0022.oracle.com (aserv0022.oracle.com [141.146.126.234]) by aserp2130.oracle.com with ESMTP id 2phasdhh0p-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sat, 22 Dec 2018 22:30:37 +0000 Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id wBMMUadv012434 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sat, 22 Dec 2018 22:30:36 GMT Received: from abhmp0007.oracle.com (abhmp0007.oracle.com [141.146.116.13]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id wBMMUZZw013491; Sat, 22 Dec 2018 22:30:35 GMT Received: from monkey.oracle.com (/50.38.38.67) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Sat, 22 Dec 2018 14:30:35 -0800 From: Mike Kravetz To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Michal Hocko , Hugh Dickins , Naoya Horiguchi , "Aneesh Kumar K . V" , Andrea Arcangeli , "Kirill A . Shutemov" , Davidlohr Bueso , Prakash Sangappa , Andrew Morton , Mike Kravetz , stable@vger.kernel.org Subject: [PATCH v3 2/2] hugetlbfs: Use i_mmap_rwsem to fix page fault/truncate race Date: Sat, 22 Dec 2018 14:30:13 -0800 Message-Id: <20181222223013.22193-3-mike.kravetz@oracle.com> X-Mailer: git-send-email 2.17.2 In-Reply-To: <20181222223013.22193-1-mike.kravetz@oracle.com> References: <20181222223013.22193-1-mike.kravetz@oracle.com> X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9115 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=972 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1812220204 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: X-Virus-Scanned: ClamAV using ClamSMTP hugetlbfs page faults can race with truncate and hole punch operations. Current code in the page fault path attempts to handle this by 'backing out' operations if we encounter the race. One obvious omission in the current code is removing a page newly added to the page cache. This is pretty straight forward to address, but there is a more subtle and difficult issue of backing out hugetlb reservations. To handle this correctly, the 'reservation state' before page allocation needs to be noted so that it can be properly backed out. There are four distinct possibilities for reservation state: shared/reserved, shared/no-resv, private/reserved and private/no-resv. Backing out a reservation may require memory allocation which could fail so that needs to be taken into account as well. Instead of writing the required complicated code for this rare occurrence, just eliminate the race. i_mmap_rwsem is now held in read mode for the duration of page fault processing. Hold i_mmap_rwsem longer in truncation and hold punch code to cover the call to remove_inode_hugepages. With this modification, code in remove_inode_hugepages checking for races becomes 'dead' as it can not longer happen. Remove the dead code and expand comments to explain reasoning. Similarly, checks for races with truncation in the page fault path can be simplified and removed. Cc: Fixes: ebed4bfc8da8 ("hugetlb: fix absurd HugePages_Rsvd") Signed-off-by: Mike Kravetz --- fs/hugetlbfs/inode.c | 61 ++++++++++++++++++++------------------------ mm/hugetlb.c | 21 ++++++++------- 2 files changed, 38 insertions(+), 44 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 32920a10100e..a2fcea5f8225 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -383,17 +383,16 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end) * truncation is indicated by end of range being LLONG_MAX * In this case, we first scan the range and release found pages. * After releasing pages, hugetlb_unreserve_pages cleans up region/reserv - * maps and global counts. Page faults can not race with truncation - * in this routine. hugetlb_no_page() prevents page faults in the - * truncated range. It checks i_size before allocation, and again after - * with the page table lock for the page held. The same lock must be - * acquired to unmap a page. + * maps and global counts. * hole punch is indicated if end is not LLONG_MAX * In the hole punch case we scan the range and release found pages. * Only when releasing a page is the associated region/reserv map * deleted. The region/reserv map for ranges without associated - * pages are not modified. Page faults can race with hole punch. - * This is indicated if we find a mapped page. + * pages are not modified. + * + * Callers of this routine must hold the i_mmap_rwsem in write mode to prevent + * races with page faults. + * * Note: If the passed end of range value is beyond the end of file, but * not LLONG_MAX this routine still performs a hole punch operation. */ @@ -423,32 +422,14 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, for (i = 0; i < pagevec_count(&pvec); ++i) { struct page *page = pvec.pages[i]; - u32 hash; index = page->index; - hash = hugetlb_fault_mutex_hash(h, current->mm, - &pseudo_vma, - mapping, index, 0); - mutex_lock(&hugetlb_fault_mutex_table[hash]); - /* - * If page is mapped, it was faulted in after being - * unmapped in caller. Unmap (again) now after taking - * the fault mutex. The mutex will prevent faults - * until we finish removing the page. - * - * This race can only happen in the hole punch case. - * Getting here in a truncate operation is a bug. + * A mapped page is impossible as callers should unmap + * all references before calling. And, i_mmap_rwsem + * prevents the creation of additional mappings. */ - if (unlikely(page_mapped(page))) { - BUG_ON(truncate_op); - - i_mmap_lock_write(mapping); - hugetlb_vmdelete_list(&mapping->i_mmap, - index * pages_per_huge_page(h), - (index + 1) * pages_per_huge_page(h)); - i_mmap_unlock_write(mapping); - } + VM_BUG_ON(page_mapped(page)); lock_page(page); /* @@ -470,7 +451,6 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, } unlock_page(page); - mutex_unlock(&hugetlb_fault_mutex_table[hash]); } huge_pagevec_release(&pvec); cond_resched(); @@ -482,9 +462,20 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, static void hugetlbfs_evict_inode(struct inode *inode) { + struct address_space *mapping = inode->i_mapping; struct resv_map *resv_map; + /* + * The vfs layer guarantees that there are no other users of this + * inode. Therefore, it would be safe to call remove_inode_hugepages + * without holding i_mmap_rwsem. We acquire and hold here to be + * consistent with other callers. Since there will be no contention + * on the semaphore, overhead is negligible. + */ + i_mmap_lock_write(mapping); remove_inode_hugepages(inode, 0, LLONG_MAX); + i_mmap_unlock_write(mapping); + resv_map = (struct resv_map *)inode->i_mapping->private_data; /* root inode doesn't have the resv_map, so we should check it */ if (resv_map) @@ -505,8 +496,8 @@ static int hugetlb_vmtruncate(struct inode *inode, loff_t offset) i_mmap_lock_write(mapping); if (!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)) hugetlb_vmdelete_list(&mapping->i_mmap, pgoff, 0); - i_mmap_unlock_write(mapping); remove_inode_hugepages(inode, offset, LLONG_MAX); + i_mmap_unlock_write(mapping); return 0; } @@ -540,8 +531,8 @@ static long hugetlbfs_punch_hole(struct inode *inode, loff_t offset, loff_t len) hugetlb_vmdelete_list(&mapping->i_mmap, hole_start >> PAGE_SHIFT, hole_end >> PAGE_SHIFT); - i_mmap_unlock_write(mapping); remove_inode_hugepages(inode, hole_start, hole_end); + i_mmap_unlock_write(mapping); inode_unlock(inode); } @@ -624,7 +615,11 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset, /* addr is the offset within the file (zero based) */ addr = index * hpage_size; - /* mutex taken here, fault path and hole punch */ + /* + * fault mutex taken here, protects against fault path + * and hole punch. inode_lock previously taken protects + * against truncation. + */ hash = hugetlb_fault_mutex_hash(h, mm, &pseudo_vma, mapping, index, addr); mutex_lock(&hugetlb_fault_mutex_table[hash]); diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 2a3162030167..cfd9790b01e3 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3757,16 +3757,16 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, } /* - * Use page lock to guard against racing truncation - * before we get page_table_lock. + * We can not race with truncation due to holding i_mmap_rwsem. + * Check once here for faults beyond end of file. */ + size = i_size_read(mapping->host) >> huge_page_shift(h); + if (idx >= size) + goto out; + retry: page = find_lock_page(mapping, idx); if (!page) { - size = i_size_read(mapping->host) >> huge_page_shift(h); - if (idx >= size) - goto out; - /* * Check for page in userfault range */ @@ -3856,9 +3856,6 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, } ptl = huge_pte_lock(h, mm, ptep); - size = i_size_read(mapping->host) >> huge_page_shift(h); - if (idx >= size) - goto backout; ret = 0; if (!huge_pte_none(huge_ptep_get(ptep))) @@ -3961,8 +3958,10 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, /* * Acquire i_mmap_rwsem before calling huge_pte_alloc and hold - * until finished with ptep. This prevents huge_pmd_unshare from - * being called elsewhere and making the ptep no longer valid. + * until finished with ptep. This serves two purposes: + * 1) It prevents huge_pmd_unshare from being called elsewhere + * and making the ptep no longer valid. + * 2) It synchronizes us with file truncation. * * ptep could have already be assigned via huge_pte_offset. That * is OK, as huge_pte_alloc will return the same value unless