5 files changed, 20 insertions, 88 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index aedc1b183cf9..df2e7dd5ff17 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3238,7 +3238,6 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
         struct page *ptepage;
         unsigned long addr;
         int cow;
-        struct address_space *mapping = vma->vm_file->f_mapping;
         struct hstate *h = hstate_vma(vma);
         unsigned long sz = huge_page_size(h);
         struct mmu_notifier_range range;
@@ -3250,23 +3249,13 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
                 mmu_notifier_range_init(&range, src, vma->vm_start,
                                         vma->vm_end);
                 mmu_notifier_invalidate_range_start(&range);
-        } 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;
@@ -3337,8 +3326,6 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
 
         if (cow)
                 mmu_notifier_invalidate_range_end(&range);
-        else
-                i_mmap_unlock_read(mapping);
 
         return ret;
 }
@@ -3784,18 +3771,14 @@ retry:
                         };
 
                         /*
-                         * hugetlb_fault_mutex and i_mmap_rwsem must be
-                         * dropped before handling userfault.  Reacquire
-                         * after handling fault to make calling code simpler.
+                         * hugetlb_fault_mutex 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;
                 }
@@ -3943,11 +3926,6 @@ 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);
@@ -3955,31 +3933,20 @@ 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;
-        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;
-        }
+        idx = vma_hugecache_offset(h, vma, haddr);
 
         /*
          * 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]);
 
@@ -4067,7 +4034,6 @@ out_ptl:
         }
 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
@@ -4672,12 +4638,10 @@ 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.
- *
- * 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).
+ * 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.
  */
 pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
 {
@@ -4694,6 +4658,7 @@ 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;
@@ -4723,6 +4688,7 @@ 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;
 }
 
@@ -4733,7 +4699,7 @@ out:
  * 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 and i_mmap_rwsem held in write mode.
+ * called with page table lock held.
  *
  * 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 6379fff1a5ff..7c72f2a95785 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -966,7 +966,7 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn,
         enum ttu_flags ttu = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
         struct address_space *mapping;
         LIST_HEAD(tokill);
-        bool unmap_success = true;
+        bool unmap_success;
         int kill = 1, forcekill;
         struct page *hpage = *hpagep;
         bool mlocked = PageMlocked(hpage);
@@ -1028,19 +1028,7 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn,
         if (kill)
                 collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED);
 
-        if (!PageHuge(hpage)) {
-                unmap_success = try_to_unmap(hpage, ttu);
-        } else if (mapping) {
-                /*
-                 * 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);
-        }
+        unmap_success = try_to_unmap(hpage, ttu);
         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 ccf8966caf6f..a16b15090df3 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1324,19 +1324,8 @@ 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_RMAP_LOCKED);
-                i_mmap_unlock_write(mapping);
+                        TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
                 page_was_mapped = 1;
         }
 
diff --git a/mm/rmap.c b/mm/rmap.c
index 21a26cf51114..68a1a5b869a5 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -25,7 +25,6 @@
  *     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)
@@ -1379,9 +1378,6 @@ 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, &range.start,
                                                      &range.end);
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 065c1ce191c4..d59b5a73dfb3 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -267,14 +267,10 @@ retry:
                 VM_BUG_ON(dst_addr & ~huge_page_mask(h));
 
                 /*
-                 * 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.
+                 * Serialize via hugetlb_fault_mutex
                  */
-                mapping = dst_vma->vm_file->f_mapping;
-                i_mmap_lock_read(mapping);
                 idx = linear_page_index(dst_vma, dst_addr);
+                mapping = dst_vma->vm_file->f_mapping;
                 hash = hugetlb_fault_mutex_hash(h, dst_mm, dst_vma, mapping,
                                                                 idx, dst_addr);
                 mutex_lock(&hugetlb_fault_mutex_table[hash]);
@@ -283,7 +279,6 @@ retry:
                 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;
                 }
 
@@ -291,7 +286,6 @@ retry:
                 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;
                 }
 
@@ -299,7 +293,6 @@ retry:
                                                 dst_addr, src_addr, &page);
 
                 mutex_unlock(&hugetlb_fault_mutex_table[hash]);
-                i_mmap_unlock_read(mapping);
                 vm_alloc_shared = vm_shared;
 
                 cond_resched();