ext4: refactor punch hole code

Move common code in ext4_ind_punch_hole() and ext4_ext_punch_hole()
into ext4_punch_hole().  This saves over 150 lines of code.

This also fixes a potential bug when the punch_hole() code is racing
against indirect-to-extents or extents-to-indirect migation.  We are
currently using i_mutex to protect against changes to the inode flag;
specifically, the append-only, immutable, and extents inode flags.  So
we need to take i_mutex before deciding whether to use the
extents-specific or indirect-specific punch_hole code.

Also, there was a missing call to ext4_inode_block_unlocked_dio() in
the indirect punch codepath.  This was added in commit 02d262dffcf4c
to block DIO readers racing against the punch operation in the
codepath for extent-mapped inodes, but it was missing for
indirect-block mapped inodes.  One of the advantages of refactoring
the code is that it makes such oversights much less likely.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 175 insertions, 5 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index a4ffb470fbf3..9bda50aa34e2 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3566,20 +3566,190 @@ int ext4_can_truncate(struct inode *inode)
 int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
 {
         struct inode *inode = file_inode(file);
+        struct super_block *sb = inode->i_sb;
+        ext4_lblk_t first_block, stop_block;
+        struct address_space *mapping = inode->i_mapping;
+        loff_t first_page, last_page, page_len;
+        loff_t first_page_offset, last_page_offset;
+        handle_t *handle;
+        unsigned int credits;
+        int ret = 0;
+
         if (!S_ISREG(inode->i_mode))
                 return -EOPNOTSUPP;
 
-        if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
-                return ext4_ind_punch_hole(file, offset, length);
-
-        if (EXT4_SB(inode->i_sb)->s_cluster_ratio > 1) {
+        if (EXT4_SB(sb)->s_cluster_ratio > 1) {
                 /* TODO: Add support for bigalloc file systems */
                 return -EOPNOTSUPP;
         }
 
         trace_ext4_punch_hole(inode, offset, length);
 
-        return ext4_ext_punch_hole(file, offset, length);
+        /*
+         * Write out all dirty pages to avoid race conditions
+         * Then release them.
+         */
+        if (mapping->nrpages && mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
+                ret = filemap_write_and_wait_range(mapping, offset,
+                                                   offset + length - 1);
+                if (ret)
+                        return ret;
+        }
+
+        mutex_lock(&inode->i_mutex);
+        /* It's not possible punch hole on append only file */
+        if (IS_APPEND(inode) || IS_IMMUTABLE(inode)) {
+                ret = -EPERM;
+                goto out_mutex;
+        }
+        if (IS_SWAPFILE(inode)) {
+                ret = -ETXTBSY;
+                goto out_mutex;
+        }
+
+        /* No need to punch hole beyond i_size */
+        if (offset >= inode->i_size)
+                goto out_mutex;
+
+        /*
+         * If the hole extends beyond i_size, set the hole
+         * to end after the page that contains i_size
+         */
+        if (offset + length > inode->i_size) {
+                length = inode->i_size +
+                   PAGE_CACHE_SIZE - (inode->i_size & (PAGE_CACHE_SIZE - 1)) -
+                   offset;
+        }
+
+        first_page = (offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+        last_page = (offset + length) >> PAGE_CACHE_SHIFT;
+
+        first_page_offset = first_page << PAGE_CACHE_SHIFT;
+        last_page_offset = last_page << PAGE_CACHE_SHIFT;
+
+        /* Now release the pages */
+        if (last_page_offset > first_page_offset) {
+                truncate_pagecache_range(inode, first_page_offset,
+                                         last_page_offset - 1);
+        }
+
+        /* Wait all existing dio workers, newcomers will block on i_mutex */
+        ext4_inode_block_unlocked_dio(inode);
+        ret = ext4_flush_unwritten_io(inode);
+        if (ret)
+                goto out_dio;
+        inode_dio_wait(inode);
+
+        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
+                credits = ext4_writepage_trans_blocks(inode);
+        else
+                credits = ext4_blocks_for_truncate(inode);
+        handle = ext4_journal_start(inode, EXT4_HT_TRUNCATE, credits);
+        if (IS_ERR(handle)) {
+                ret = PTR_ERR(handle);
+                ext4_std_error(sb, ret);
+                goto out_dio;
+        }
+
+        /*
+         * Now we need to zero out the non-page-aligned data in the
+         * pages at the start and tail of the hole, and unmap the
+         * buffer heads for the block aligned regions of the page that
+         * were completely zeroed.
+         */
+        if (first_page > last_page) {
+                /*
+                 * If the file space being truncated is contained
+                 * within a page just zero out and unmap the middle of
+                 * that page
+                 */
+                ret = ext4_discard_partial_page_buffers(handle,
+                        mapping, offset, length, 0);
+
+                if (ret)
+                        goto out_stop;
+        } else {
+                /*
+                 * zero out and unmap the partial page that contains
+                 * the start of the hole
+                 */
+                page_len = first_page_offset - offset;
+                if (page_len > 0) {
+                        ret = ext4_discard_partial_page_buffers(handle, mapping,
+                                                offset, page_len, 0);
+                        if (ret)
+                                goto out_stop;
+                }
+
+                /*
+                 * zero out and unmap the partial page that contains
+                 * the end of the hole
+                 */
+                page_len = offset + length - last_page_offset;
+                if (page_len > 0) {
+                        ret = ext4_discard_partial_page_buffers(handle, mapping,
+                                        last_page_offset, page_len, 0);
+                        if (ret)
+                                goto out_stop;
+                }
+        }
+
+        /*
+         * If i_size is contained in the last page, we need to
+         * unmap and zero the partial page after i_size
+         */
+        if (inode->i_size >> PAGE_CACHE_SHIFT == last_page &&
+           inode->i_size % PAGE_CACHE_SIZE != 0) {
+                page_len = PAGE_CACHE_SIZE -
+                        (inode->i_size & (PAGE_CACHE_SIZE - 1));
+
+                if (page_len > 0) {
+                        ret = ext4_discard_partial_page_buffers(handle,
+                                        mapping, inode->i_size, page_len, 0);
+
+                        if (ret)
+                                goto out_stop;
+                }
+        }
+
+        first_block = (offset + sb->s_blocksize - 1) >>
+                EXT4_BLOCK_SIZE_BITS(sb);
+        stop_block = (offset + length) >> EXT4_BLOCK_SIZE_BITS(sb);
+
+        /* If there are no blocks to remove, return now */
+        if (first_block >= stop_block)
+                goto out_stop;
+
+        down_write(&EXT4_I(inode)->i_data_sem);
+        ext4_discard_preallocations(inode);
+
+        ret = ext4_es_remove_extent(inode, first_block,
+                                    stop_block - first_block);
+        if (ret) {
+                up_write(&EXT4_I(inode)->i_data_sem);
+                goto out_stop;
+        }
+
+        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
+                ret = ext4_ext_remove_space(inode, first_block,
+                                            stop_block - 1);
+        else
+                ret = ext4_free_hole_blocks(handle, inode, first_block,
+                                            stop_block);
+
+        ext4_discard_preallocations(inode);
+        if (IS_SYNC(inode))
+                ext4_handle_sync(handle);
+        up_write(&EXT4_I(inode)->i_data_sem);
+        inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
+        ext4_mark_inode_dirty(handle, inode);
+out_stop:
+        ext4_journal_stop(handle);
+out_dio:
+        ext4_inode_resume_unlocked_dio(inode);
+out_mutex:
+        mutex_unlock(&inode->i_mutex);
+        return ret;
 }
 
 /*