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 <jack@xxxxxxx>
---
fs/ext4/ext4.h | 10 ----
fs/ext4/extents.c | 35 +++-----------
fs/ext4/inode.c | 133 ++++++++++++++++++++++++++++--------------------------
3 files changed, 74 insertions(+), 104 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 80cc3914b6ad..29d51505a9d2 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1513,16 +1513,6 @@ static inline void ext4_set_io_unwritten_flag(struct inode *inode,
}
}
-static inline ext4_io_end_t *ext4_inode_aio(struct inode *inode)
-{
- return inode->i_private;
-}
-
-static inline void ext4_inode_aio_set(struct inode *inode, ext4_io_end_t *io)
-{
- inode->i_private = io;
-}
-
/*
* Inode dynamic state flags
*/
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 0ffabaf90aa5..1742e60e229c 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;
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 506180729faf..ef411c4f11f8 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -768,18 +768,16 @@ int ext4_dio_get_block(struct inode *inode, sector_t iblock,
}
/*
- * Get block function for DIO writes when we create unwritten extent if
+ * Get block function for AIO DIO writes when we create unwritten extent if
* blocks are not allocated yet. The extent will be converted to written
* after IO is complete.
*/
-static int ext4_dio_get_block_unwritten(struct inode *inode, sector_t iblock,
- struct buffer_head *bh_result, int create)
+static int ext4_dio_get_block_unwritten_async(struct inode *inode,
+ sector_t iblock, struct buffer_head *bh_result, int create)
{
handle_t *handle;
int ret;
- ext4_debug("ext4_dio_get_block_unwritten: inode %lu, create flag %d\n",
- inode->i_ino, create);
/* We don't expect handle for direct IO */
WARN_ON_ONCE(ext4_journal_current_handle());
@@ -789,16 +787,62 @@ static int ext4_dio_get_block_unwritten(struct inode *inode, sector_t iblock,
ret = _ext4_get_block(inode, iblock, bh_result,
EXT4_GET_BLOCKS_IO_CREATE_EXT);
ext4_journal_stop(handle);
- if (!ret && buffer_unwritten(bh_result)) {
- ext4_io_end_t *io_end = ext4_inode_aio(inode);
+ /*
+ * When doing DIO using unwritten extents, we need io_end to convert
+ * unwritten extents to written on IO completion. We allocate io_end
+ * once we spot unwritten extent and store it in b_private. Generic
+ * DIO code keeps b_private set and furthermore passes the value to
+ * our completion callback in 'private' argument.
+ */
+ if (!ret && buffer_unwritten(bh_result)) {
+ if (!bh_result->b_private) {
+ ext4_io_end_t *io_end;
+
+ io_end = ext4_init_io_end(inode, GFP_KERNEL);
+ if (!io_end)
+ return -ENOMEM;
+ bh_result->b_private = io_end;
+ ext4_set_io_unwritten_flag(inode, io_end);
+ }
set_buffer_defer_completion(bh_result);
- WARN_ON_ONCE(io_end && !(io_end->flag & EXT4_IO_END_UNWRITTEN));
}
return ret;
}
+/*
+ * Get block function for non-AIO DIO writes when we create unwritten extent if
+ * blocks are not allocated yet. The extent will be converted to written
+ * after IO is complete from ext4_ext_direct_IO() function.
+ */
+static int ext4_dio_get_block_unwritten_sync(struct inode *inode,
+ sector_t iblock, struct buffer_head *bh_result, int create)
+{
+ handle_t *handle;
+ int ret;
+
+ /* We don't expect handle for direct IO */
+ WARN_ON_ONCE(ext4_journal_current_handle());
+
+ handle = start_dio_trans(inode, bh_result);
+ if (IS_ERR(handle))
+ return PTR_ERR(handle);
+ ret = _ext4_get_block(inode, iblock, bh_result,
+ EXT4_GET_BLOCKS_IO_CREATE_EXT);
+ ext4_journal_stop(handle);
+
+ /*
+ * Mark inode as having pending DIO writes to unwritten extents.
+ * ext4_ext_direct_IO() checks this flag and converts extents to
+ * written.
+ */
+ if (!ret && buffer_unwritten(bh_result))
+ ext4_set_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
+
+ return ret;
+}
+
static int ext4_dio_get_block_overwrite(struct inode *inode, sector_t iblock,
struct buffer_head *bh_result, int create)
{
@@ -3214,7 +3258,7 @@ out:
static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
ssize_t size, void *private)
{
- ext4_io_end_t *io_end = iocb->private;
+ ext4_io_end_t *io_end = private;
/* if not async direct IO just return */
if (!io_end)
@@ -3222,10 +3266,8 @@ static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
ext_debug("ext4_end_io_dio(): io_end 0x%p "
"for inode %lu, iocb 0x%p, offset %llu, size %zd\n",
- iocb->private, io_end->inode->i_ino, iocb, offset,
- size);
+ io_end, io_end->inode->i_ino, iocb, offset, size);
- iocb->private = NULL;
io_end->offset = offset;
io_end->size = size;
ext4_put_io_end(io_end);
@@ -3261,7 +3303,6 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
get_block_t *get_block_func = NULL;
int dio_flags = 0;
loff_t final_size = offset + count;
- ext4_io_end_t *io_end = NULL;
/* Use the old path for reads and writes beyond i_size. */
if (iov_iter_rw(iter) != WRITE || final_size > inode->i_size)
@@ -3286,16 +3327,17 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
/*
* We could direct write to holes and fallocate.
*
- * Allocated blocks to fill the hole are marked as
- * unwritten to prevent parallel buffered read to expose
- * the stale data before DIO complete the data IO.
+ * Allocated blocks to fill the hole are marked as unwritten to prevent
+ * parallel buffered read to expose the stale data before DIO complete
+ * the data IO.
*
- * As to previously fallocated extents, ext4 get_block will
- * just simply mark the buffer mapped but still keep the
- * extents unwritten.
+ * As to previously fallocated extents, ext4 get_block will just simply
+ * mark the buffer mapped but still keep the extents unwritten.
*
- * For non AIO case, we will convert those unwritten extents
- * to written after return back from blockdev_direct_IO.
+ * For non AIO case, we will convert those unwritten extents to written
+ * after return back from blockdev_direct_IO. That way we save us from
+ * allocating io_end structure and also the overhead of offloading
+ * the extent convertion to a workqueue.
*
* For async DIO, the conversion needs to be deferred when the
* IO is completed. The ext4 end_io callback function will be
@@ -3303,30 +3345,13 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
* case, we allocate an io_end structure to hook to the iocb.
*/
iocb->private = NULL;
- if (overwrite) {
+ if (overwrite)
get_block_func = ext4_dio_get_block_overwrite;
+ else if (is_sync_kiocb(iocb)) {
+ get_block_func = ext4_dio_get_block_unwritten_sync;
+ dio_flags = DIO_LOCKING;
} else {
- ext4_inode_aio_set(inode, NULL);
- if (!is_sync_kiocb(iocb)) {
- io_end = ext4_init_io_end(inode, GFP_NOFS);
- if (!io_end) {
- ret = -ENOMEM;
- goto retake_lock;
- }
- /*
- * Grab reference for DIO. Will be dropped in
- * ext4_end_io_dio()
- */
- iocb->private = ext4_get_io_end(io_end);
- /*
- * we save the io structure for current async direct
- * IO, so that later ext4_map_blocks() could flag the
- * io structure whether there is a unwritten extents
- * needs to be converted when IO is completed.
- */
- ext4_inode_aio_set(inode, io_end);
- }
- get_block_func = ext4_dio_get_block_unwritten;
+ get_block_func = ext4_dio_get_block_unwritten_async;
dio_flags = DIO_LOCKING;
}
#ifdef CONFIG_EXT4_FS_ENCRYPTION
@@ -3341,27 +3366,6 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
get_block_func,
ext4_end_io_dio, NULL, dio_flags);
- /*
- * Put our reference to io_end. This can free the io_end structure e.g.
- * in sync IO case or in case of error. It can even perform extent
- * conversion if all bios we submitted finished before we got here.
- * Note that in that case iocb->private can be already set to NULL
- * here.
- */
- if (io_end) {
- ext4_inode_aio_set(inode, NULL);
- ext4_put_io_end(io_end);
- /*
- * When no IO was submitted ext4_end_io_dio() was not
- * called so we have to put iocb's reference.
- */
- if (ret <= 0 && ret != -EIOCBQUEUED && iocb->private) {
- WARN_ON(iocb->private != io_end);
- WARN_ON(io_end->flag & EXT4_IO_END_UNWRITTEN);
- ext4_put_io_end(io_end);
- iocb->private = NULL;
- }
- }
if (ret > 0 && !overwrite && ext4_test_inode_state(inode,
EXT4_STATE_DIO_UNWRITTEN)) {
int err;
@@ -3376,7 +3380,6 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
ext4_clear_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
}
-retake_lock:
if (iov_iter_rw(iter) == WRITE)
inode_dio_end(inode);
/* take i_mutex locking again if we do a ovewrite dio */
--
2.6.2
--
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