1 files changed, 77 insertions, 40 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 8f419cff9e34..af68b15a8fc1 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -85,7 +85,7 @@ static struct vfsmount *shm_mnt;
  * a time): we would prefer not to enlarge the shmem inode just for that.
  */
 struct shmem_falloc {
-        int     mode;           /* FALLOC_FL mode currently operating */
+        wait_queue_head_t *waitq; /* faults into hole wait for punch to end */
         pgoff_t start;          /* start of range currently being fallocated */
         pgoff_t next;           /* the next page offset to be fallocated */
         pgoff_t nr_falloced;    /* how many new pages have been fallocated */
@@ -468,23 +468,20 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
                 return;
 
         index = start;
-        for ( ; ; ) {
+        while (index < end) {
                 cond_resched();
 
                 pvec.nr = find_get_entries(mapping, index,
                                 min(end - index, (pgoff_t)PAGEVEC_SIZE),
                                 pvec.pages, indices);
                 if (!pvec.nr) {
-                        if (index == start || unfalloc)
+                        /* If all gone or hole-punch or unfalloc, we're done */
+                        if (index == start || end != -1)
                                 break;
+                        /* But if truncating, restart to make sure all gone */
                         index = start;
                         continue;
                 }
-                if ((index == start || unfalloc) && indices[0] >= end) {
-                        pagevec_remove_exceptionals(&pvec);
-                        pagevec_release(&pvec);
-                        break;
-                }
                 mem_cgroup_uncharge_start();
                 for (i = 0; i < pagevec_count(&pvec); i++) {
                         struct page *page = pvec.pages[i];
@@ -496,8 +493,12 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
                         if (radix_tree_exceptional_entry(page)) {
                                 if (unfalloc)
                                         continue;
-                                nr_swaps_freed += !shmem_free_swap(mapping,
-                                                                index, page);
+                                if (shmem_free_swap(mapping, index, page)) {
+                                        /* Swap was replaced by page: retry */
+                                        index--;
+                                        break;
+                                }
+                                nr_swaps_freed++;
                                 continue;
                         }
 
@@ -506,6 +507,11 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
                                 if (page->mapping == mapping) {
                                         VM_BUG_ON_PAGE(PageWriteback(page), page);
                                         truncate_inode_page(mapping, page);
+                                } else {
+                                        /* Page was replaced by swap: retry */
+                                        unlock_page(page);
+                                        index--;
+                                        break;
                                 }
                         }
                         unlock_page(page);
@@ -760,7 +766,7 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
                         spin_lock(&inode->i_lock);
                         shmem_falloc = inode->i_private;
                         if (shmem_falloc &&
-                            !shmem_falloc->mode &&
+                            !shmem_falloc->waitq &&
                             index >= shmem_falloc->start &&
                             index < shmem_falloc->next)
                                 shmem_falloc->nr_unswapped++;
@@ -1029,6 +1035,9 @@ repeat:
                 goto failed;
         }
 
+        if (page && sgp == SGP_WRITE)
+                mark_page_accessed(page);
+
         /* fallocated page? */
         if (page && !PageUptodate(page)) {
                 if (sgp != SGP_READ)
@@ -1110,6 +1119,9 @@ repeat:
                 shmem_recalc_inode(inode);
                 spin_unlock(&info->lock);
 
+                if (sgp == SGP_WRITE)
+                        mark_page_accessed(page);
+
                 delete_from_swap_cache(page);
                 set_page_dirty(page);
                 swap_free(swap);
@@ -1136,6 +1148,9 @@ repeat:
 
                 __SetPageSwapBacked(page);
                 __set_page_locked(page);
+                if (sgp == SGP_WRITE)
+                        init_page_accessed(page);
+
                 error = mem_cgroup_charge_file(page, current->mm,
                                                 gfp & GFP_RECLAIM_MASK);
                 if (error)
@@ -1239,38 +1254,58 @@ static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
          * Trinity finds that probing a hole which tmpfs is punching can
          * prevent the hole-punch from ever completing: which in turn
          * locks writers out with its hold on i_mutex.  So refrain from
-         * faulting pages into the hole while it's being punched, and
-         * wait on i_mutex to be released if vmf->flags permits.
+         * faulting pages into the hole while it's being punched.  Although
+         * shmem_undo_range() does remove the additions, it may be unable to
+         * keep up, as each new page needs its own unmap_mapping_range() call,
+         * and the i_mmap tree grows ever slower to scan if new vmas are added.
+         *
+         * It does not matter if we sometimes reach this check just before the
+         * hole-punch begins, so that one fault then races with the punch:
+         * we just need to make racing faults a rare case.
+         *
+         * The implementation below would be much simpler if we just used a
+         * standard mutex or completion: but we cannot take i_mutex in fault,
+         * and bloating every shmem inode for this unlikely case would be sad.
          */
         if (unlikely(inode->i_private)) {
                 struct shmem_falloc *shmem_falloc;
 
                 spin_lock(&inode->i_lock);
                 shmem_falloc = inode->i_private;
-                if (!shmem_falloc ||
-                    shmem_falloc->mode != FALLOC_FL_PUNCH_HOLE ||
-                    vmf->pgoff < shmem_falloc->start ||
-                    vmf->pgoff >= shmem_falloc->next)
-                        shmem_falloc = NULL;
-                spin_unlock(&inode->i_lock);
-                /*
-                 * i_lock has protected us from taking shmem_falloc seriously
-                 * once return from shmem_fallocate() went back up that stack.
-                 * i_lock does not serialize with i_mutex at all, but it does
-                 * not matter if sometimes we wait unnecessarily, or sometimes
-                 * miss out on waiting: we just need to make those cases rare.
-                 */
-                if (shmem_falloc) {
+                if (shmem_falloc &&
+                    shmem_falloc->waitq &&
+                    vmf->pgoff >= shmem_falloc->start &&
+                    vmf->pgoff < shmem_falloc->next) {
+                        wait_queue_head_t *shmem_falloc_waitq;
+                        DEFINE_WAIT(shmem_fault_wait);
+
+                        ret = VM_FAULT_NOPAGE;
                         if ((vmf->flags & FAULT_FLAG_ALLOW_RETRY) &&
                            !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
+                                /* It's polite to up mmap_sem if we can */
                                 up_read(&vma->vm_mm->mmap_sem);
-                                mutex_lock(&inode->i_mutex);
-                                mutex_unlock(&inode->i_mutex);
-                                return VM_FAULT_RETRY;
+                                ret = VM_FAULT_RETRY;
                         }
-                        /* cond_resched? Leave that to GUP or return to user */
-                        return VM_FAULT_NOPAGE;
+
+                        shmem_falloc_waitq = shmem_falloc->waitq;
+                        prepare_to_wait(shmem_falloc_waitq, &shmem_fault_wait,
+                                        TASK_UNINTERRUPTIBLE);
+                        spin_unlock(&inode->i_lock);
+                        schedule();
+
+                        /*
+                         * shmem_falloc_waitq points into the shmem_fallocate()
+                         * stack of the hole-punching task: shmem_falloc_waitq
+                         * is usually invalid by the time we reach here, but
+                         * finish_wait() does not dereference it in that case;
+                         * though i_lock needed lest racing with wake_up_all().
+                         */
+                        spin_lock(&inode->i_lock);
+                        finish_wait(shmem_falloc_waitq, &shmem_fault_wait);
+                        spin_unlock(&inode->i_lock);
+                        return ret;
                 }
+                spin_unlock(&inode->i_lock);
         }
 
         error = shmem_getpage(inode, vmf->pgoff, &vmf->page, SGP_CACHE, &ret);
@@ -1412,13 +1447,9 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
                         loff_t pos, unsigned len, unsigned flags,
                         struct page **pagep, void **fsdata)
 {
-        int ret;
         struct inode *inode = mapping->host;
         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
-        ret = shmem_getpage(inode, index, pagep, SGP_WRITE, NULL);
-        if (ret == 0 && *pagep)
-                init_page_accessed(*pagep);
-        return ret;
+        return shmem_getpage(inode, index, pagep, SGP_WRITE, NULL);
 }
 
 static int
@@ -1769,13 +1800,13 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 
         mutex_lock(&inode->i_mutex);
 
-        shmem_falloc.mode = mode & ~FALLOC_FL_KEEP_SIZE;
-
         if (mode & FALLOC_FL_PUNCH_HOLE) {
                 struct address_space *mapping = file->f_mapping;
                 loff_t unmap_start = round_up(offset, PAGE_SIZE);
                 loff_t unmap_end = round_down(offset + len, PAGE_SIZE) - 1;
+                DECLARE_WAIT_QUEUE_HEAD_ONSTACK(shmem_falloc_waitq);
 
+                shmem_falloc.waitq = &shmem_falloc_waitq;
                 shmem_falloc.start = unmap_start >> PAGE_SHIFT;
                 shmem_falloc.next = (unmap_end + 1) >> PAGE_SHIFT;
                 spin_lock(&inode->i_lock);
@@ -1787,8 +1818,13 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
                                             1 + unmap_end - unmap_start, 0);
                 shmem_truncate_range(inode, offset, offset + len - 1);
                 /* No need to unmap again: hole-punching leaves COWed pages */
+
+                spin_lock(&inode->i_lock);
+                inode->i_private = NULL;
+                wake_up_all(&shmem_falloc_waitq);
+                spin_unlock(&inode->i_lock);
                 error = 0;
-                goto undone;
+                goto out;
         }
 
         /* We need to check rlimit even when FALLOC_FL_KEEP_SIZE */
@@ -1804,6 +1840,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
                 goto out;
         }
 
+        shmem_falloc.waitq = NULL;
         shmem_falloc.start = start;
         shmem_falloc.next  = start;
         shmem_falloc.nr_falloced = 0;