Message-Id: <20170922215508.73407-4-drosen@google.com>
Date:   Fri, 22 Sep 2017 14:55:06 -0700
From:   Daniel Rosenberg <drosen@...gle.com>
To:     Phillip Lougher <phillip@...ashfs.org.uk>,
        linux-kernel@...r.kernel.org
Cc:     adrien@...ischi.me, Adrien Schildknecht <adriens@...gle.com>,
        Daniel Rosenberg <drosen@...gle.com>
Subject: [PATCH 3/5] Squashfs: replace buffer_head with BIO

From: Adrien Schildknecht <adriens@...gle.com>

The 'll_rw_block' has been deprecated and BIO is now the basic container
for block I/O within the kernel.

Switching to BIO offers 2 advantages:
  1/ It removes synchronous wait for the up-to-date buffers: SquashFS
     now deals with decompressions/copies asynchronously.
     Implementing an asynchronous mechanism to read data is needed to
     efficiently implement .readpages().
  2/ Prior to this patch, merging the read requests entirely depends on
     the IO scheduler. SquashFS has more information than the IO
     scheduler about what could be merged. Moreover, merging the reads
     at the FS level means that we rely less on the IO scheduler.

Signed-off-by: Adrien Schildknecht <adriens@...gle.com>
Signed-off-by: Daniel Rosenberg <drosen@...gle.com>
---
 fs/squashfs/block.c       | 522 +++++++++++++++++++++++++++++++++-------------
 fs/squashfs/file_direct.c | 195 ++++++-----------
 fs/squashfs/squashfs.h    |   4 +
 fs/squashfs/super.c       |   7 +
 4 files changed, 456 insertions(+), 272 deletions(-)

diff --git a/fs/squashfs/block.c b/fs/squashfs/block.c
index 2751476e6b6e..252dfc82ae72 100644
--- a/fs/squashfs/block.c
+++ b/fs/squashfs/block.c
@@ -32,6 +32,8 @@
 #include <linux/string.h>
 #include <linux/buffer_head.h>
 #include <linux/bio.h>
+#include <linux/pagemap.h>
+#include <linux/workqueue.h>
 
 #include "squashfs_fs.h"
 #include "squashfs_fs_sb.h"
@@ -39,45 +41,357 @@
 #include "decompressor.h"
 #include "page_actor.h"
 
-/*
- * Read the metadata block length, this is stored in the first two
- * bytes of the metadata block.
- */
-static struct buffer_head *get_block_length(struct super_block *sb,
-			u64 *cur_index, int *offset, int *length)
+static struct workqueue_struct *squashfs_read_wq;
+
+struct squashfs_read_request {
+	struct super_block *sb;
+	u64 index;
+	int length;
+	int compressed;
+	int offset;
+	u64 read_end;
+	struct squashfs_page_actor *output;
+	enum {
+		SQUASHFS_COPY,
+		SQUASHFS_DECOMPRESS,
+		SQUASHFS_METADATA,
+	} data_processing;
+	bool synchronous;
+
+	/*
+	 * If the read is synchronous, it is possible to retrieve information
+	 * about the request by setting these pointers.
+	 */
+	int *res;
+	int *bytes_read;
+	int *bytes_uncompressed;
+
+	int nr_buffers;
+	struct buffer_head **bh;
+	struct work_struct offload;
+};
+
+struct squashfs_bio_request {
+	struct buffer_head **bh;
+	int nr_buffers;
+};
+
+static int squashfs_bio_submit(struct squashfs_read_request *req);
+
+int squashfs_init_read_wq(void)
+{
+	squashfs_read_wq = create_workqueue("SquashFS read wq");
+	return !!squashfs_read_wq;
+}
+
+void squashfs_destroy_read_wq(void)
 {
-	struct squashfs_sb_info *msblk = sb->s_fs_info;
+	flush_workqueue(squashfs_read_wq);
+	destroy_workqueue(squashfs_read_wq);
+}
+
+static void free_read_request(struct squashfs_read_request *req, int error)
+{
+	if (!req->synchronous)
+		squashfs_page_actor_free(req->output, error);
+	if (req->res)
+		*(req->res) = error;
+	kfree(req->bh);
+	kfree(req);
+}
+
+static void squashfs_process_blocks(struct squashfs_read_request *req)
+{
+	int error = 0;
+	int bytes, i, length;
+	struct squashfs_sb_info *msblk = req->sb->s_fs_info;
+	struct squashfs_page_actor *actor = req->output;
+	struct buffer_head **bh = req->bh;
+	int nr_buffers = req->nr_buffers;
+
+	for (i = 0; i < nr_buffers; ++i) {
+		if (!bh[i])
+			continue;
+		wait_on_buffer(bh[i]);
+		if (!buffer_uptodate(bh[i]))
+			error = -EIO;
+	}
+	if (error)
+		goto cleanup;
+
+	if (req->data_processing == SQUASHFS_METADATA) {
+		/* Extract the length of the metadata block */
+		if (req->offset != msblk->devblksize - 1) {
+			length = le16_to_cpup((__le16 *)
+					(bh[0]->b_data + req->offset));
+		} else {
+			length = (unsigned char)bh[0]->b_data[req->offset];
+			length |= (unsigned char)bh[1]->b_data[0] << 8;
+		}
+		req->compressed = SQUASHFS_COMPRESSED(length);
+		req->data_processing = req->compressed ? SQUASHFS_DECOMPRESS
+						       : SQUASHFS_COPY;
+		length = SQUASHFS_COMPRESSED_SIZE(length);
+		if (req->index + length + 2 > req->read_end) {
+			for (i = 0; i < nr_buffers; ++i)
+				put_bh(bh[i]);
+			kfree(bh);
+			req->length = length;
+			req->index += 2;
+			squashfs_bio_submit(req);
+			return;
+		}
+		req->length = length;
+		req->offset = (req->offset + 2) % PAGE_SIZE;
+		if (req->offset < 2) {
+			put_bh(bh[0]);
+			++bh;
+			--nr_buffers;
+		}
+	}
+	if (req->bytes_read)
+		*(req->bytes_read) = req->length;
+
+	if (req->data_processing == SQUASHFS_COPY) {
+		squashfs_bh_to_actor(bh, nr_buffers, req->output, req->offset,
+			req->length, msblk->devblksize);
+	} else if (req->data_processing == SQUASHFS_DECOMPRESS) {
+		req->length = squashfs_decompress(msblk, bh, nr_buffers,
+			req->offset, req->length, actor);
+		if (req->length < 0) {
+			error = -EIO;
+			goto cleanup;
+		}
+	}
+
+	/* Last page may have trailing bytes not filled */
+	bytes = req->length % PAGE_SIZE;
+	if (bytes && actor->page[actor->pages - 1])
+		zero_user_segment(actor->page[actor->pages - 1], bytes,
+				  PAGE_SIZE);
+
+cleanup:
+	if (req->bytes_uncompressed)
+		*(req->bytes_uncompressed) = req->length;
+	if (error) {
+		for (i = 0; i < nr_buffers; ++i)
+			if (bh[i])
+				put_bh(bh[i]);
+	}
+	free_read_request(req, error);
+}
+
+static void read_wq_handler(struct work_struct *work)
+{
+	squashfs_process_blocks(container_of(work,
+		    struct squashfs_read_request, offload));
+}
+
+static void squashfs_bio_end_io(struct bio *bio)
+{
+	int i;
+	int error = bio->bi_status;
+	struct squashfs_bio_request *bio_req = bio->bi_private;
+
+	bio_put(bio);
+
+	for (i = 0; i < bio_req->nr_buffers; ++i) {
+		if (!bio_req->bh[i])
+			continue;
+		if (!error)
+			set_buffer_uptodate(bio_req->bh[i]);
+		else
+			clear_buffer_uptodate(bio_req->bh[i]);
+		unlock_buffer(bio_req->bh[i]);
+	}
+	kfree(bio_req);
+}
+
+static int actor_getblks(struct squashfs_read_request *req, u64 block)
+{
+	int i;
+
+	req->bh = kmalloc_array(req->nr_buffers, sizeof(*(req->bh)), GFP_NOIO);
+	if (!req->bh)
+		return -ENOMEM;
+
+	for (i = 0; i < req->nr_buffers; ++i) {
+		req->bh[i] = sb_getblk(req->sb, block + i);
+		if (!req->bh[i]) {
+			while (--i) {
+				if (req->bh[i])
+					put_bh(req->bh[i]);
+			}
+			return -1;
+		}
+	}
+	return 0;
+}
+
+static int squashfs_bio_submit(struct squashfs_read_request *req)
+{
+	struct bio *bio = NULL;
 	struct buffer_head *bh;
+	struct squashfs_bio_request *bio_req = NULL;
+	int b = 0, prev_block = 0;
+	struct squashfs_sb_info *msblk = req->sb->s_fs_info;
+
+	u64 read_start = round_down(req->index, msblk->devblksize);
+	u64 read_end = round_up(req->index + req->length, msblk->devblksize);
+	sector_t block = read_start >> msblk->devblksize_log2;
+	sector_t block_end = read_end >> msblk->devblksize_log2;
+	int offset = read_start - round_down(req->index, PAGE_SIZE);
+	int nr_buffers = block_end - block;
+	int blksz = msblk->devblksize;
+	int bio_max_pages = nr_buffers > BIO_MAX_PAGES ? BIO_MAX_PAGES
+						       : nr_buffers;
+
+	/* Setup the request */
+	req->read_end = read_end;
+	req->offset = req->index - read_start;
+	req->nr_buffers = nr_buffers;
+	if (actor_getblks(req, block) < 0)
+		goto getblk_failed;
 
-	bh = sb_bread(sb, *cur_index);
-	if (bh == NULL)
-		return NULL;
-
-	if (msblk->devblksize - *offset == 1) {
-		*length = (unsigned char) bh->b_data[*offset];
-		put_bh(bh);
-		bh = sb_bread(sb, ++(*cur_index));
-		if (bh == NULL)
-			return NULL;
-		*length |= (unsigned char) bh->b_data[0] << 8;
-		*offset = 1;
-	} else {
-		*length = (unsigned char) bh->b_data[*offset] |
-			(unsigned char) bh->b_data[*offset + 1] << 8;
-		*offset += 2;
-
-		if (*offset == msblk->devblksize) {
-			put_bh(bh);
-			bh = sb_bread(sb, ++(*cur_index));
-			if (bh == NULL)
-				return NULL;
-			*offset = 0;
+	/* Create and submit the BIOs */
+	for (b = 0; b < nr_buffers; ++b, offset += blksz) {
+		bh = req->bh[b];
+		if (!bh || !trylock_buffer(bh))
+			continue;
+		if (buffer_uptodate(bh)) {
+			unlock_buffer(bh);
+			continue;
 		}
+		offset %= PAGE_SIZE;
+
+		/* Append the buffer to the current BIO if it is contiguous */
+		if (bio && bio_req && prev_block + 1 == b) {
+			if (bio_add_page(bio, bh->b_page, blksz, offset)) {
+				bio_req->nr_buffers += 1;
+				prev_block = b;
+				continue;
+			}
+		}
+
+		/* Otherwise, submit the current BIO and create a new one */
+		if (bio)
+			submit_bio(bio);
+		bio_req = kcalloc(1, sizeof(struct squashfs_bio_request),
+				  GFP_NOIO);
+		if (!bio_req)
+			goto req_alloc_failed;
+		bio_req->bh = &req->bh[b];
+		bio = bio_alloc(GFP_NOIO, bio_max_pages);
+		if (!bio)
+			goto bio_alloc_failed;
+		bio_set_dev(bio, req->sb->s_bdev);
+		bio->bi_iter.bi_sector = (block + b)
+				       << (msblk->devblksize_log2 - 9);
+		bio_set_op_attrs(bio, REQ_OP_READ, 0);
+		bio->bi_private = bio_req;
+		bio->bi_end_io = squashfs_bio_end_io;
+
+		bio_add_page(bio, bh->b_page, blksz, offset);
+		bio_req->nr_buffers += 1;
+		prev_block = b;
 	}
+	if (bio)
+		submit_bio(bio);
 
-	return bh;
+	if (req->synchronous)
+		squashfs_process_blocks(req);
+	else {
+		INIT_WORK(&req->offload, read_wq_handler);
+		schedule_work(&req->offload);
+	}
+	return 0;
+
+bio_alloc_failed:
+	kfree(bio_req);
+req_alloc_failed:
+	unlock_buffer(bh);
+	while (--nr_buffers >= b)
+		if (req->bh[nr_buffers])
+			put_bh(req->bh[nr_buffers]);
+	while (--b >= 0)
+		if (req->bh[b])
+			wait_on_buffer(req->bh[b]);
+getblk_failed:
+	free_read_request(req, -ENOMEM);
+	return -ENOMEM;
+}
+
+static int read_metadata_block(struct squashfs_read_request *req,
+			       u64 *next_index)
+{
+	int ret, error, bytes_read = 0, bytes_uncompressed = 0;
+	struct squashfs_sb_info *msblk = req->sb->s_fs_info;
+
+	if (req->index + 2 > msblk->bytes_used) {
+		free_read_request(req, -EINVAL);
+		return -EINVAL;
+	}
+	req->length = 2;
+
+	/* Do not read beyond the end of the device */
+	if (req->index + req->length > msblk->bytes_used)
+		req->length = msblk->bytes_used - req->index;
+	req->data_processing = SQUASHFS_METADATA;
+
+	/*
+	 * Reading metadata is always synchronous because we don't know the
+	 * length in advance and the function is expected to update
+	 * 'next_index' and return the length.
+	 */
+	req->synchronous = true;
+	req->res = &error;
+	req->bytes_read = &bytes_read;
+	req->bytes_uncompressed = &bytes_uncompressed;
+
+	TRACE("Metadata block @ 0x%llx, %scompressed size %d, src size %d\n",
+	      req->index, req->compressed ? "" : "un", bytes_read,
+	      req->output->length);
+
+	ret = squashfs_bio_submit(req);
+	if (ret)
+		return ret;
+	if (error)
+		return error;
+	if (next_index)
+		*next_index += 2 + bytes_read;
+	return bytes_uncompressed;
 }
 
+static int read_data_block(struct squashfs_read_request *req, int length,
+			   u64 *next_index, bool synchronous)
+{
+	int ret, error = 0, bytes_uncompressed = 0, bytes_read = 0;
+
+	req->compressed = SQUASHFS_COMPRESSED_BLOCK(length);
+	req->length = length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
+	req->data_processing = req->compressed ? SQUASHFS_DECOMPRESS
+					       : SQUASHFS_COPY;
+
+	req->synchronous = synchronous;
+	if (synchronous) {
+		req->res = &error;
+		req->bytes_read = &bytes_read;
+		req->bytes_uncompressed = &bytes_uncompressed;
+	}
+
+	TRACE("Data block @ 0x%llx, %scompressed size %d, src size %d\n",
+	      req->index, req->compressed ? "" : "un", req->length,
+	      req->output->length);
+
+	ret = squashfs_bio_submit(req);
+	if (ret)
+		return ret;
+	if (synchronous)
+		ret = error ? error : bytes_uncompressed;
+	if (next_index)
+		*next_index += length;
+	return ret;
+}
 
 /*
  * Read and decompress a metadata block or datablock.  Length is non-zero
@@ -88,128 +402,50 @@ static struct buffer_head *get_block_length(struct super_block *sb,
  * generated a larger block - this does occasionally happen with compression
  * algorithms).
  */
-int squashfs_read_data(struct super_block *sb, u64 index, int length,
-		u64 *next_index, struct squashfs_page_actor *output)
+static int __squashfs_read_data(struct super_block *sb, u64 index, int length,
+	u64 *next_index, struct squashfs_page_actor *output, bool sync)
 {
-	struct squashfs_sb_info *msblk = sb->s_fs_info;
-	struct buffer_head **bh;
-	int offset = index & ((1 << msblk->devblksize_log2) - 1);
-	u64 cur_index = index >> msblk->devblksize_log2;
-	int bytes, compressed, b = 0, k = 0, avail, i;
+	struct squashfs_read_request *req;
 
-	bh = kcalloc(((output->length + msblk->devblksize - 1)
-		>> msblk->devblksize_log2) + 1, sizeof(*bh), GFP_KERNEL);
-	if (bh == NULL)
+	req = kcalloc(1, sizeof(struct squashfs_read_request), GFP_KERNEL);
+	if (!req) {
+		if (!sync)
+			squashfs_page_actor_free(output, -ENOMEM);
 		return -ENOMEM;
+	}
 
-	if (length) {
-		/*
-		 * Datablock.
-		 */
-		bytes = -offset;
-		compressed = SQUASHFS_COMPRESSED_BLOCK(length);
-		length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
-		if (next_index)
-			*next_index = index + length;
-
-		TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
-			index, compressed ? "" : "un", length, output->length);
-
-		if (length < 0 || length > output->length ||
-				(index + length) > msblk->bytes_used)
-			goto read_failure;
-
-		for (b = 0; bytes < length; b++, cur_index++) {
-			bh[b] = sb_getblk(sb, cur_index);
-			if (bh[b] == NULL)
-				goto block_release;
-			bytes += msblk->devblksize;
-		}
-		ll_rw_block(REQ_OP_READ, 0, b, bh);
-	} else {
-		/*
-		 * Metadata block.
-		 */
-		if ((index + 2) > msblk->bytes_used)
-			goto read_failure;
-
-		bh[0] = get_block_length(sb, &cur_index, &offset, &length);
-		if (bh[0] == NULL)
-			goto read_failure;
-		b = 1;
-
-		bytes = msblk->devblksize - offset;
-		compressed = SQUASHFS_COMPRESSED(length);
-		length = SQUASHFS_COMPRESSED_SIZE(length);
-		if (next_index)
-			*next_index = index + length + 2;
+	req->sb = sb;
+	req->index = index;
+	req->output = output;
 
-		TRACE("Block @ 0x%llx, %scompressed size %d\n", index,
-				compressed ? "" : "un", length);
+	if (next_index)
+		*next_index = index;
 
-		if (length < 0 || length > output->length ||
-					(index + length) > msblk->bytes_used)
-			goto block_release;
+	if (length)
+		length = read_data_block(req, length, next_index, sync);
+	else
+		length = read_metadata_block(req, next_index);
 
-		for (; bytes < length; b++) {
-			bh[b] = sb_getblk(sb, ++cur_index);
-			if (bh[b] == NULL)
-				goto block_release;
-			bytes += msblk->devblksize;
-		}
-		ll_rw_block(REQ_OP_READ, 0, b - 1, bh + 1);
+	if (length < 0) {
+		ERROR("squashfs_read_data failed to read block 0x%llx\n",
+		      (unsigned long long)index);
+		return -EIO;
 	}
 
-	for (i = 0; i < b; i++) {
-		wait_on_buffer(bh[i]);
-		if (!buffer_uptodate(bh[i]))
-			goto block_release;
-	}
-
-	if (compressed) {
-		length = squashfs_decompress(msblk, bh, b, offset, length,
-			output);
-		if (length < 0)
-			goto read_failure;
-	} else {
-		/*
-		 * Block is uncompressed.
-		 */
-		int in, pg_offset = 0;
-		void *data = squashfs_first_page(output);
-
-		for (bytes = length; k < b; k++) {
-			in = min(bytes, msblk->devblksize - offset);
-			bytes -= in;
-			while (in) {
-				if (pg_offset == PAGE_SIZE) {
-					data = squashfs_next_page(output);
-					pg_offset = 0;
-				}
-				avail = min_t(int, in, PAGE_SIZE -
-						pg_offset);
-				memcpy(data + pg_offset, bh[k]->b_data + offset,
-						avail);
-				in -= avail;
-				pg_offset += avail;
-				offset += avail;
-			}
-			offset = 0;
-			put_bh(bh[k]);
-		}
-		squashfs_finish_page(output);
-	}
-
-	kfree(bh);
 	return length;
+}
+
+int squashfs_read_data(struct super_block *sb, u64 index, int length,
+	u64 *next_index, struct squashfs_page_actor *output)
+{
+	return __squashfs_read_data(sb, index, length, next_index, output,
+				    true);
+}
 
-block_release:
-	for (; k < b; k++)
-		put_bh(bh[k]);
+int squashfs_read_data_async(struct super_block *sb, u64 index, int length,
+	u64 *next_index, struct squashfs_page_actor *output)
+{
 
-read_failure:
-	ERROR("squashfs_read_data failed to read block 0x%llx\n",
-					(unsigned long long) index);
-	kfree(bh);
-	return -EIO;
+	return __squashfs_read_data(sb, index, length, next_index, output,
+				    false);
 }
diff --git a/fs/squashfs/file_direct.c b/fs/squashfs/file_direct.c
index 4642b869d931..74b8f381320b 100644
--- a/fs/squashfs/file_direct.c
+++ b/fs/squashfs/file_direct.c
@@ -20,157 +20,94 @@
 #include "squashfs.h"
 #include "page_actor.h"
 
-static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
-	int pages, struct page **page);
+static void release_actor_pages(struct page **page, int pages, int error)
+{
+	int i;
 
-/* Read separately compressed datablock directly into page cache */
-int squashfs_readpage_block(struct page *target_page, u64 block, int bsize)
+	for (i = 0; i < pages; i++) {
+		if (!page[i])
+			continue;
+		flush_dcache_page(page[i]);
+		if (!error)
+			SetPageUptodate(page[i]);
+		else {
+			SetPageError(page[i]);
+			zero_user_segment(page[i], 0, PAGE_SIZE);
+		}
+		unlock_page(page[i]);
+		put_page(page[i]);
+	}
+	kfree(page);
+}
 
+/*
+ * Create a "page actor" which will kmap and kunmap the
+ * page cache pages appropriately within the decompressor
+ */
+static struct squashfs_page_actor *actor_from_page_cache(
+	struct page *target_page, int start_index, int nr_pages)
 {
-	struct inode *inode = target_page->mapping->host;
-	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
-
-	int file_end = (i_size_read(inode) - 1) >> PAGE_SHIFT;
-	int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
-	int start_index = target_page->index & ~mask;
-	int end_index = start_index | mask;
-	int i, n, pages, missing_pages, bytes, res = -ENOMEM;
+	int i, n;
 	struct page **page;
 	struct squashfs_page_actor *actor;
-	void *pageaddr;
-
-	if (end_index > file_end)
-		end_index = file_end;
 
-	pages = end_index - start_index + 1;
-
-	page = kmalloc_array(pages, sizeof(void *), GFP_KERNEL);
-	if (page == NULL)
-		return res;
-
-	/*
-	 * Create a "page actor" which will kmap and kunmap the
-	 * page cache pages appropriately within the decompressor
-	 */
-	actor = squashfs_page_actor_init(page, pages, 0, NULL);
-	if (actor == NULL)
-		goto out;
-
-	/* Try to grab all the pages covered by the Squashfs block */
-	for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) {
-		page[i] = (n == target_page->index) ? target_page :
-			grab_cache_page_nowait(target_page->mapping, n);
-
-		if (page[i] == NULL) {
-			missing_pages++;
-			continue;
+	page = kmalloc_array(nr_pages, sizeof(void *), GFP_KERNEL);
+	if (!page)
+		return NULL;
+
+	/* Try to grab all the pages covered by the SquashFS block */
+	for (i = 0, n = start_index; i < nr_pages; i++, n++) {
+		if (target_page->index == n) {
+			page[i] = target_page;
+		} else {
+			page[i] = grab_cache_page_nowait(target_page->mapping,
+							 n);
+			if (page[i] == NULL)
+				continue;
 		}
 
 		if (PageUptodate(page[i])) {
 			unlock_page(page[i]);
 			put_page(page[i]);
 			page[i] = NULL;
-			missing_pages++;
 		}
 	}
 
-	if (missing_pages) {
-		/*
-		 * Couldn't get one or more pages, this page has either
-		 * been VM reclaimed, but others are still in the page cache
-		 * and uptodate, or we're racing with another thread in
-		 * squashfs_readpage also trying to grab them.  Fall back to
-		 * using an intermediate buffer.
-		 */
-		res = squashfs_read_cache(target_page, block, bsize, pages,
-								page);
-		if (res < 0)
-			goto mark_errored;
-
-		goto out;
-	}
-
-	/* Decompress directly into the page cache buffers */
-	res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
-	if (res < 0)
-		goto mark_errored;
-
-	/* Last page may have trailing bytes not filled */
-	bytes = res % PAGE_SIZE;
-	if (bytes) {
-		pageaddr = kmap_atomic(page[pages - 1]);
-		memset(pageaddr + bytes, 0, PAGE_SIZE - bytes);
-		kunmap_atomic(pageaddr);
+	actor = squashfs_page_actor_init(page, nr_pages, 0,
+			release_actor_pages);
+	if (!actor) {
+		release_actor_pages(page, nr_pages, -ENOMEM);
+		kfree(page);
+		return NULL;
 	}
-
-	/* Mark pages as uptodate, unlock and release */
-	for (i = 0; i < pages; i++) {
-		flush_dcache_page(page[i]);
-		SetPageUptodate(page[i]);
-		unlock_page(page[i]);
-		if (page[i] != target_page)
-			put_page(page[i]);
-	}
-
-	kfree(actor);
-	kfree(page);
-
-	return 0;
-
-mark_errored:
-	/* Decompression failed, mark pages as errored.  Target_page is
-	 * dealt with by the caller
-	 */
-	for (i = 0; i < pages; i++) {
-		if (page[i] == NULL || page[i] == target_page)
-			continue;
-		flush_dcache_page(page[i]);
-		SetPageError(page[i]);
-		unlock_page(page[i]);
-		put_page(page[i]);
-	}
-
-out:
-	squashfs_page_actor_free(actor, 0);
-	kfree(page);
-	return res;
+	return actor;
 }
 
+/* Read separately compressed datablock directly into page cache */
+int squashfs_readpage_block(struct page *target_page, u64 block, int bsize)
 
-static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
-	int pages, struct page **page)
 {
-	struct inode *i = target_page->mapping->host;
-	struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb,
-						 block, bsize);
-	int bytes = buffer->length, res = buffer->error, n, offset = 0;
-	void *pageaddr;
-
-	if (res) {
-		ERROR("Unable to read page, block %llx, size %x\n", block,
-			bsize);
-		goto out;
-	}
+	struct inode *inode = target_page->mapping->host;
+	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
 
-	for (n = 0; n < pages && bytes > 0; n++,
-			bytes -= PAGE_SIZE, offset += PAGE_SIZE) {
-		int avail = min_t(int, bytes, PAGE_SIZE);
+	int file_end = (i_size_read(inode) - 1) >> PAGE_SHIFT;
+	int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
+	int start_index = target_page->index & ~mask;
+	int end_index = start_index | mask;
+	int pages, res = -ENOMEM;
+	struct squashfs_page_actor *actor;
 
-		if (page[n] == NULL)
-			continue;
+	if (end_index > file_end)
+		end_index = file_end;
+	pages = end_index - start_index + 1;
 
-		pageaddr = kmap_atomic(page[n]);
-		squashfs_copy_data(pageaddr, buffer, offset, avail);
-		memset(pageaddr + avail, 0, PAGE_SIZE - avail);
-		kunmap_atomic(pageaddr);
-		flush_dcache_page(page[n]);
-		SetPageUptodate(page[n]);
-		unlock_page(page[n]);
-		if (page[n] != target_page)
-			put_page(page[n]);
-	}
+	actor = actor_from_page_cache(target_page, start_index, pages);
+
+	if (!actor)
+		return -ENOMEM;
 
-out:
-	squashfs_cache_put(buffer);
-	return res;
+	get_page(target_page);
+	res = squashfs_read_data_async(inode->i_sb, block, bsize, NULL,
+				       actor);
+	return res < 0 ? res : 0;
 }
diff --git a/fs/squashfs/squashfs.h b/fs/squashfs/squashfs.h
index 887d6d270080..66d7194563b6 100644
--- a/fs/squashfs/squashfs.h
+++ b/fs/squashfs/squashfs.h
@@ -28,8 +28,12 @@
 #define WARNING(s, args...)	pr_warn("SQUASHFS: "s, ## args)
 
 /* block.c */
+extern int squashfs_init_read_wq(void);
+extern void squashfs_destroy_read_wq(void);
 extern int squashfs_read_data(struct super_block *, u64, int, u64 *,
 				struct squashfs_page_actor *);
+extern int squashfs_read_data_async(struct super_block *, u64, int, u64 *,
+				struct squashfs_page_actor *);
 
 /* cache.c */
 extern struct squashfs_cache *squashfs_cache_init(char *, int, int);
diff --git a/fs/squashfs/super.c b/fs/squashfs/super.c
index cf01e15a7b16..e2a0a7342bf8 100644
--- a/fs/squashfs/super.c
+++ b/fs/squashfs/super.c
@@ -444,9 +444,15 @@ static int __init init_squashfs_fs(void)
 	if (err)
 		return err;
 
+	if (!squashfs_init_read_wq()) {
+		destroy_inodecache();
+		return -ENOMEM;
+	}
+
 	err = register_filesystem(&squashfs_fs_type);
 	if (err) {
 		destroy_inodecache();
+		squashfs_destroy_read_wq();
 		return err;
 	}
 
@@ -460,6 +466,7 @@ static void __exit exit_squashfs_fs(void)
 {
 	unregister_filesystem(&squashfs_fs_type);
 	destroy_inodecache();
+	squashfs_destroy_read_wq();
 }
 
 
-- 
2.14.1.821.g8fa685d3b7-goog

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