From 109811c20fb8ec46e2ed01750214a32a9163d164 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Tue, 8 Mar 2016 23:36:46 -0500 Subject: ext4: simplify io_end handling for AIO DIO When mapping blocks for direct IO, we allocate io_end structure before mapping blocks and store pointer to it in the inode. This creates a requirement that any AIO DIO using io_end must be protected by i_mutex. This created problems in the past with dioread_nolock mode which was corrupting io_end pointers. Also io_end is allocated unnecessarily in case where we don't need to convert any extents (which is a common case for example when overwriting file). We fix the problem by allocating io_end only once we return unwritten extent from block mapping function for AIO DIO (so we can save some pointless io_end allocations) and we pass pointer to it in bh->b_private which generic DIO code later passes to our end IO callback. That way we remove any need for global pointer to io_end structure and thus fix the races. The downside of this change is that the checking for unwritten IO in flight in ext4_extents_can_be_merged() is more racy since we now increment i_unwritten / set EXT4_STATE_DIO_UNWRITTEN only after dropping i_data_sem. However the check has been racy already before because ext4_writepages() already increment i_unwritten after dropping i_data_sem and reserved blocks save us from hitting ENOSPC in the worst case. Signed-off-by: Jan Kara --- fs/ext4/extents.c | 35 ++++++----------------------------- 1 file changed, 6 insertions(+), 29 deletions(-) (limited to 'fs/ext4/extents.c') diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 73a48c1657a1..f1b3c2586a1a 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -1736,6 +1736,12 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1, */ if (ext1_ee_len + ext2_ee_len > EXT_INIT_MAX_LEN) return 0; + /* + * The check for IO to unwritten extent is somewhat racy as we + * increment i_unwritten / set EXT4_STATE_DIO_UNWRITTEN only after + * dropping i_data_sem. But reserved blocks should save us in that + * case. + */ if (ext4_ext_is_unwritten(ex1) && (ext4_test_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN) || atomic_read(&EXT4_I(inode)->i_unwritten) || @@ -4007,7 +4013,6 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode, struct ext4_ext_path *path = *ppath; int ret = 0; int err = 0; - ext4_io_end_t *io = ext4_inode_aio(inode); ext_debug("ext4_ext_handle_unwritten_extents: inode %lu, logical " "block %llu, max_blocks %u, flags %x, allocated %u\n", @@ -4030,15 +4035,6 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode, flags | EXT4_GET_BLOCKS_CONVERT); if (ret <= 0) goto out; - /* - * Flag the inode(non aio case) or end_io struct (aio case) - * that this IO needs to conversion to written when IO is - * completed - */ - if (io) - ext4_set_io_unwritten_flag(inode, io); - else - ext4_set_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN); map->m_flags |= EXT4_MAP_UNWRITTEN; goto out; } @@ -4283,9 +4279,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode, unsigned int allocated = 0, offset = 0; unsigned int allocated_clusters = 0; struct ext4_allocation_request ar; - ext4_io_end_t *io = ext4_inode_aio(inode); ext4_lblk_t cluster_offset; - int set_unwritten = 0; bool map_from_cluster = false; ext_debug("blocks %u/%u requested for inode %lu\n", @@ -4482,15 +4476,6 @@ got_allocated_blocks: if (flags & EXT4_GET_BLOCKS_UNWRIT_EXT){ ext4_ext_mark_unwritten(&newex); map->m_flags |= EXT4_MAP_UNWRITTEN; - /* - * io_end structure was created for every IO write to an - * unwritten extent. To avoid unnecessary conversion, - * here we flag the IO that really needs the conversion. - * For non asycn direct IO case, flag the inode state - * that we need to perform conversion when IO is done. - */ - if (flags & EXT4_GET_BLOCKS_PRE_IO) - set_unwritten = 1; } err = 0; @@ -4501,14 +4486,6 @@ got_allocated_blocks: err = ext4_ext_insert_extent(handle, inode, &path, &newex, flags); - if (!err && set_unwritten) { - if (io) - ext4_set_io_unwritten_flag(inode, io); - else - ext4_set_inode_state(inode, - EXT4_STATE_DIO_UNWRITTEN); - } - if (err && free_on_err) { int fb_flags = flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE ? EXT4_FREE_BLOCKS_NO_QUOT_UPDATE : 0; -- cgit v1.2.3