Btrfs: btrfs_page_mkwrite: Reserve space in sectorsized units

In subpagesize-blocksize scenario, if i_size occurs in a block which is not
the last block in the page, then the space to be reserved should be calculated
appropriately.

Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 30 insertions, 5 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 0bfd7fb2e83c..ad27f5d1a4a1 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8802,15 +8802,28 @@ int btrfs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
         loff_t size;
         int ret;
         int reserved = 0;
+        u64 reserved_space;
         u64 page_start;
         u64 page_end;
+        u64 end;
+
+        reserved_space = PAGE_CACHE_SIZE;
 
         sb_start_pagefault(inode->i_sb);
         page_start = page_offset(page);
         page_end = page_start + PAGE_CACHE_SIZE - 1;
+        end = page_end;
 
+        /*
+         * Reserving delalloc space after obtaining the page lock can lead to
+         * deadlock. For example, if a dirty page is locked by this function
+         * and the call to btrfs_delalloc_reserve_space() ends up triggering
+         * dirty page write out, then the btrfs_writepage() function could
+         * end up waiting indefinitely to get a lock on the page currently
+         * being processed by btrfs_page_mkwrite() function.
+         */
         ret = btrfs_delalloc_reserve_space(inode, page_start,
-                                           PAGE_CACHE_SIZE);
+                                           reserved_space);
         if (!ret) {
                 ret = file_update_time(vma->vm_file);
                 reserved = 1;
@@ -8844,7 +8857,7 @@ again:
          * we can't set the delalloc bits if there are pending ordered
          * extents.  Drop our locks and wait for them to finish
          */
-        ordered = btrfs_lookup_ordered_extent(inode, page_start);
+        ordered = btrfs_lookup_ordered_range(inode, page_start, page_end);
         if (ordered) {
                 unlock_extent_cached(io_tree, page_start, page_end,
                                      &cached_state, GFP_NOFS);
@@ -8854,6 +8867,18 @@ again:
                 goto again;
         }
 
+        if (page->index == ((size - 1) >> PAGE_CACHE_SHIFT)) {
+                reserved_space = round_up(size - page_start, root->sectorsize);
+                if (reserved_space < PAGE_CACHE_SIZE) {
+                        end = page_start + reserved_space - 1;
+                        spin_lock(&BTRFS_I(inode)->lock);
+                        BTRFS_I(inode)->outstanding_extents++;
+                        spin_unlock(&BTRFS_I(inode)->lock);
+                        btrfs_delalloc_release_space(inode, page_start,
+                                                PAGE_CACHE_SIZE - reserved_space);
+                }
+        }
+
         /*
          * XXX - page_mkwrite gets called every time the page is dirtied, even
          * if it was already dirty, so for space accounting reasons we need to
@@ -8861,12 +8886,12 @@ again:
          * is probably a better way to do this, but for now keep consistent with
          * prepare_pages in the normal write path.
          */
-        clear_extent_bit(&BTRFS_I(inode)->io_tree, page_start, page_end,
+        clear_extent_bit(&BTRFS_I(inode)->io_tree, page_start, end,
                           EXTENT_DIRTY | EXTENT_DELALLOC |
                           EXTENT_DO_ACCOUNTING | EXTENT_DEFRAG,
                           0, 0, &cached_state, GFP_NOFS);
 
-        ret = btrfs_set_extent_delalloc(inode, page_start, page_end,
+        ret = btrfs_set_extent_delalloc(inode, page_start, end,
                                         &cached_state);
         if (ret) {
                 unlock_extent_cached(io_tree, page_start, page_end,
@@ -8905,7 +8930,7 @@ out_unlock:
         }
         unlock_page(page);
 out:
-        btrfs_delalloc_release_space(inode, page_start, PAGE_CACHE_SIZE);
+        btrfs_delalloc_release_space(inode, page_start, reserved_space);
 out_noreserve:
         sb_end_pagefault(inode->i_sb);
         return ret;