Revert "btrfs: zstd: fix and simplify the inline extent decompression"

This reverts commit 1e7f6de.

It causes my machine to not even boot, and Klara Modin reports that the
cause is that small zstd-compressed files return garbage when read.

Reported-by: Klara Modin <klarasmodin@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/CABq1_vj4GpUeZpVG49OHCo-3sdbe2-2ROcu_xDvUG-6-5zPRXg@mail.gmail.com/
Reported-and-bisected-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: David Sterba <dsterba@suse.com>
Cc: Qu Wenruo <wqu@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/btrfs/compression.h

@@ -169,7 +169,7 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
 		unsigned long *total_in, unsigned long *total_out);
 int zstd_decompress_bio(struct list_head *ws, struct compressed_bio *cb);
 int zstd_decompress(struct list_head *ws, const u8 *data_in,
-		struct page *dest_page, unsigned long dest_pgoff, size_t srclen,
+		struct page *dest_page, unsigned long start_byte, size_t srclen,
 		size_t destlen);
 void zstd_init_workspace_manager(void);
 void zstd_cleanup_workspace_manager(void);

fs/btrfs/zstd.c

@@ -20,7 +20,6 @@
 #include "misc.h"
 #include "compression.h"
 #include "ctree.h"
-#include "super.h"
 
 #define ZSTD_BTRFS_MAX_WINDOWLOG 17
 #define ZSTD_BTRFS_MAX_INPUT (1 << ZSTD_BTRFS_MAX_WINDOWLOG)
@@ -619,48 +618,80 @@ int zstd_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
 }
 
 int zstd_decompress(struct list_head *ws, const u8 *data_in,
-		struct page *dest_page, unsigned long dest_pgoff, size_t srclen,
+		struct page *dest_page, unsigned long start_byte, size_t srclen,
 		size_t destlen)
 {
 	struct workspace *workspace = list_entry(ws, struct workspace, list);
-	struct btrfs_fs_info *fs_info = btrfs_sb(dest_page->mapping->host->i_sb);
-	const u32 sectorsize = fs_info->sectorsize;
 	zstd_dstream *stream;
 	int ret = 0;
-	unsigned long to_copy = 0;
+	size_t ret2;
+	unsigned long total_out = 0;
+	unsigned long pg_offset = 0;
 
 	stream = zstd_init_dstream(
 			ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
 	if (!stream) {
 		pr_warn("BTRFS: zstd_init_dstream failed\n");
+		ret = -EIO;
 		goto finish;
 	}
 
+	destlen = min_t(size_t, destlen, PAGE_SIZE);
+
 	workspace->in_buf.src = data_in;
 	workspace->in_buf.pos = 0;
 	workspace->in_buf.size = srclen;
 
 	workspace->out_buf.dst = workspace->buf;
 	workspace->out_buf.pos = 0;
-	workspace->out_buf.size = sectorsize;
-
-	/*
-	 * Since both input and output buffers should not exceed one sector,
-	 * one call should end the decompression.
-	 */
-	ret = zstd_decompress_stream(stream, &workspace->out_buf, &workspace->in_buf);
-	if (zstd_is_error(ret)) {
-		pr_warn_ratelimited("BTRFS: zstd_decompress_stream return %d\n",
-				    zstd_get_error_code(ret));
-		goto finish;
+	workspace->out_buf.size = PAGE_SIZE;
+
+	ret2 = 1;
+	while (pg_offset < destlen
+	       && workspace->in_buf.pos < workspace->in_buf.size) {
+		unsigned long buf_start;
+		unsigned long buf_offset;
+		unsigned long bytes;
+
+		/* Check if the frame is over and we still need more input */
+		if (ret2 == 0) {
+			pr_debug("BTRFS: zstd_decompress_stream ended early\n");
+			ret = -EIO;
+			goto finish;
+		}
+		ret2 = zstd_decompress_stream(stream, &workspace->out_buf,
+				&workspace->in_buf);
+		if (zstd_is_error(ret2)) {
+			pr_debug("BTRFS: zstd_decompress_stream returned %d\n",
+					zstd_get_error_code(ret2));
+			ret = -EIO;
+			goto finish;
+		}
+
+		buf_start = total_out;
+		total_out += workspace->out_buf.pos;
+		workspace->out_buf.pos = 0;
+
+		if (total_out <= start_byte)
+			continue;
+
+		if (total_out > start_byte && buf_start < start_byte)
+			buf_offset = start_byte - buf_start;
+		else
+			buf_offset = 0;
+
+		bytes = min_t(unsigned long, destlen - pg_offset,
+				workspace->out_buf.size - buf_offset);
+
+		memcpy_to_page(dest_page, pg_offset,
+			       workspace->out_buf.dst + buf_offset, bytes);
+
+		pg_offset += bytes;
 	}
-	to_copy = workspace->out_buf.pos;
-	memcpy_to_page(dest_page, dest_pgoff + to_copy, workspace->out_buf.dst, to_copy);
+	ret = 0;
 finish:
-	/* Error or early end. */
-	if (unlikely(to_copy < destlen)) {
-		ret = -EIO;
-		memzero_page(dest_page, dest_pgoff + to_copy, destlen - to_copy);
+	if (pg_offset < destlen) {
+		memzero_page(dest_page, pg_offset, destlen - pg_offset);
 	}
 	return ret;
 }