[PATCH] mm: unmap_vmas with inner ptlock

Remove the page_table_lock from around the calls to unmap_vmas, and replace
the pte_offset_map in zap_pte_range by pte_offset_map_lock: all callers are
now safe to descend without page_table_lock.

Don't attempt fancy locking for hugepages, just take page_table_lock in
unmap_hugepage_range.  Which makes zap_hugepage_range, and the hugetlb test in
zap_page_range, redundant: unmap_vmas calls unmap_hugepage_range anyway.  Nor
does unmap_vmas have much use for its mm arg now.

The tlb_start_vma and tlb_end_vma in unmap_page_range are now called without
page_table_lock: if they're implemented at all, they typically come down to
flush_cache_range (usually done outside page_table_lock) and flush_tlb_range
(which we already audited for the mprotect case).

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 17 insertions, 44 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ea0826ff2663..f29b7dc02c39 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -314,6 +314,8 @@ void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
         BUG_ON(start & ~HPAGE_MASK);
         BUG_ON(end & ~HPAGE_MASK);
 
+        spin_lock(&mm->page_table_lock);
+
         /* Update high watermark before we lower rss */
         update_hiwater_rss(mm);
 
@@ -333,17 +335,9 @@ void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
                 put_page(page);
                 add_mm_counter(mm, file_rss, (int) -(HPAGE_SIZE / PAGE_SIZE));
         }
-        flush_tlb_range(vma, start, end);
-}
 
-void zap_hugepage_range(struct vm_area_struct *vma,
-                        unsigned long start, unsigned long length)
-{
-        struct mm_struct *mm = vma->vm_mm;
-
-        spin_lock(&mm->page_table_lock);
-        unmap_hugepage_range(vma, start, start + length);
         spin_unlock(&mm->page_table_lock);
+        flush_tlb_range(vma, start, end);
 }
 
 int hugetlb_prefault(struct address_space *mapping, struct vm_area_struct *vma)
diff --git a/mm/memory.c b/mm/memory.c
index 4ea89a2e3a83..622a4ef5409f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -551,10 +551,11 @@ static void zap_pte_range(struct mmu_gather *tlb,
 {
         struct mm_struct *mm = tlb->mm;
         pte_t *pte;
+        spinlock_t *ptl;
         int file_rss = 0;
         int anon_rss = 0;
 
-        pte = pte_offset_map(pmd, addr);
+        pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
         do {
                 pte_t ptent = *pte;
                 if (pte_none(ptent))
@@ -621,7 +622,7 @@ static void zap_pte_range(struct mmu_gather *tlb,
         } while (pte++, addr += PAGE_SIZE, addr != end);
 
         add_mm_rss(mm, file_rss, anon_rss);
-        pte_unmap(pte - 1);
+        pte_unmap_unlock(pte - 1, ptl);
 }
 
 static inline void zap_pmd_range(struct mmu_gather *tlb,
@@ -690,7 +691,6 @@ static void unmap_page_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
 /**
  * unmap_vmas - unmap a range of memory covered by a list of vma's
  * @tlbp: address of the caller's struct mmu_gather
- * @mm: the controlling mm_struct
  * @vma: the starting vma
  * @start_addr: virtual address at which to start unmapping
  * @end_addr: virtual address at which to end unmapping
@@ -699,10 +699,10 @@ static void unmap_page_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
  *
  * Returns the end address of the unmapping (restart addr if interrupted).
  *
- * Unmap all pages in the vma list.  Called under page_table_lock.
+ * Unmap all pages in the vma list.
  *
- * We aim to not hold page_table_lock for too long (for scheduling latency
- * reasons).  So zap pages in ZAP_BLOCK_SIZE bytecounts.  This means we need to
+ * We aim to not hold locks for too long (for scheduling latency reasons).
+ * So zap pages in ZAP_BLOCK_SIZE bytecounts.  This means we need to
  * return the ending mmu_gather to the caller.
  *
  * Only addresses between `start' and `end' will be unmapped.
@@ -714,7 +714,7 @@ static void unmap_page_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
  * ensure that any thus-far unmapped pages are flushed before unmap_vmas()
  * drops the lock and schedules.
  */
-unsigned long unmap_vmas(struct mmu_gather **tlbp, struct mm_struct *mm,
+unsigned long unmap_vmas(struct mmu_gather **tlbp,
                 struct vm_area_struct *vma, unsigned long start_addr,
                 unsigned long end_addr, unsigned long *nr_accounted,
                 struct zap_details *details)
@@ -764,19 +764,15 @@ unsigned long unmap_vmas(struct mmu_gather **tlbp, struct mm_struct *mm,
                         tlb_finish_mmu(*tlbp, tlb_start, start);
 
                         if (need_resched() ||
-                                need_lockbreak(&mm->page_table_lock) ||
                                 (i_mmap_lock && need_lockbreak(i_mmap_lock))) {
                                 if (i_mmap_lock) {
-                                        /* must reset count of rss freed */
-                                        *tlbp = tlb_gather_mmu(mm, fullmm);
+                                        *tlbp = NULL;
                                         goto out;
                                 }
-                                spin_unlock(&mm->page_table_lock);
                                 cond_resched();
-                                spin_lock(&mm->page_table_lock);
                         }
 
-                        *tlbp = tlb_gather_mmu(mm, fullmm);
+                        *tlbp = tlb_gather_mmu(vma->vm_mm, fullmm);
                         tlb_start_valid = 0;
                         zap_bytes = ZAP_BLOCK_SIZE;
                 }
@@ -800,18 +796,12 @@ unsigned long zap_page_range(struct vm_area_struct *vma, unsigned long address,
         unsigned long end = address + size;
         unsigned long nr_accounted = 0;
 
-        if (is_vm_hugetlb_page(vma)) {
-                zap_hugepage_range(vma, address, size);
-                return end;
-        }
-
         lru_add_drain();
         tlb = tlb_gather_mmu(mm, 0);
         update_hiwater_rss(mm);
-        spin_lock(&mm->page_table_lock);
-        end = unmap_vmas(&tlb, mm, vma, address, end, &nr_accounted, details);
-        spin_unlock(&mm->page_table_lock);
-        tlb_finish_mmu(tlb, address, end);
+        end = unmap_vmas(&tlb, vma, address, end, &nr_accounted, details);
+        if (tlb)
+                tlb_finish_mmu(tlb, address, end);
         return end;
 }
 
@@ -1434,13 +1424,6 @@ again:
 
         restart_addr = zap_page_range(vma, start_addr,
                                         end_addr - start_addr, details);
-
-        /*
-         * We cannot rely on the break test in unmap_vmas:
-         * on the one hand, we don't want to restart our loop
-         * just because that broke out for the page_table_lock;
-         * on the other hand, it does no test when vma is small.
-         */
         need_break = need_resched() ||
                         need_lockbreak(details->i_mmap_lock);
 
diff --git a/mm/mmap.c b/mm/mmap.c
index fa35323a3c5b..5ecc2cf3e1d7 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1673,9 +1673,7 @@ static void unmap_region(struct mm_struct *mm,
         lru_add_drain();
         tlb = tlb_gather_mmu(mm, 0);
         update_hiwater_rss(mm);
-        spin_lock(&mm->page_table_lock);
-        unmap_vmas(&tlb, mm, vma, start, end, &nr_accounted, NULL);
-        spin_unlock(&mm->page_table_lock);
+        unmap_vmas(&tlb, vma, start, end, &nr_accounted, NULL);
         vm_unacct_memory(nr_accounted);
         free_pgtables(&tlb, vma, prev? prev->vm_end: FIRST_USER_ADDRESS,
                                  next? next->vm_start: 0);
@@ -1958,9 +1956,7 @@ void exit_mmap(struct mm_struct *mm)
         tlb = tlb_gather_mmu(mm, 1);
         /* Don't update_hiwater_rss(mm) here, do_exit already did */
         /* Use -1 here to ensure all VMAs in the mm are unmapped */
-        spin_lock(&mm->page_table_lock);
-        end = unmap_vmas(&tlb, mm, vma, 0, -1, &nr_accounted, NULL);
-        spin_unlock(&mm->page_table_lock);
+        end = unmap_vmas(&tlb, vma, 0, -1, &nr_accounted, NULL);
         vm_unacct_memory(nr_accounted);
         free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, 0);
         tlb_finish_mmu(tlb, 0, end);