From: Jan Kara <jack@xxxxxxxx> Current code implementing FALLOC_FL_COLLAPSE_RANGE and FALLOC_FL_INSERT_RANGE is prone to races with buffered writes and page faults. If buffered write or write via mmap manages to squeeze between filemap_write_and_wait_range() and truncate_pagecache() in the fallocate implementations, the written data is simply discarded by truncate_pagecache() although it should have been shifted. Fix the problem by moving filemap_write_and_wait_range() call inside i_mutex and i_mmap_sem. That way we are protected against races with both buffered writes and page faults. Signed-off-by: Jan Kara <jack@xxxxxxxx> Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> Reviewed-by: Mingming Cao <mingming.cao@xxxxxxxxxx> Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx> --- fs/ext4/extents.c | 35 +++++++++++++++++++++-------------- 1 file changed, 21 insertions(+), 14 deletions(-) diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index fee4844..8d16a01 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -5423,21 +5423,7 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len) return ret; } - /* - * Need to round down offset to be aligned with page size boundary - * for page size > block size. - */ - ioffset = round_down(offset, PAGE_SIZE); - - /* Write out all dirty pages */ - ret = filemap_write_and_wait_range(inode->i_mapping, ioffset, - LLONG_MAX); - if (ret) - return ret; - - /* Take mutex lock */ mutex_lock(&inode->i_mutex); - /* * There is no need to overlap collapse range with EOF, in which case * it is effectively a truncate operation @@ -5462,6 +5448,27 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len) * page cache. */ down_write(&EXT4_I(inode)->i_mmap_sem); + /* + * Need to round down offset to be aligned with page size boundary + * for page size > block size. + */ + ioffset = round_down(offset, PAGE_SIZE); + /* + * Write tail of the last page before removed range since it will get + * removed from the page cache below. + */ + ret = filemap_write_and_wait_range(inode->i_mapping, ioffset, offset); + if (ret) + goto out_mmap; + /* + * Write data that will be shifted to preserve them when discarding + * page cache below. We are also protected from pages becoming dirty + * by i_mmap_sem. + */ + ret = filemap_write_and_wait_range(inode->i_mapping, offset + len, + LLONG_MAX); + if (ret) + goto out_mmap; truncate_pagecache(inode, ioffset); credits = ext4_writepage_trans_blocks(inode); -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html