[PATCH 6.18.y 1/2] erofs: improve decompression error reporting

29 Dec 2025

From: Gao Xiang hsiangkao@linux.alibaba.com
[ Upstream commit 831faabed8129246c9802af9ad9581a2c1e9eeb9 ]
Change the return type of decompress() from `int` to `const char *` to
provide more informative error diagnostics:
- A NULL return indicates successful decompression;
- If IS_ERR(ptr) is true, the return value encodes a standard negative
   errno (e.g., -ENOMEM, -EOPNOTSUPP) identifying the specific error;
- Otherwise, a non-NULL return points to a human-readable error string,
   and the corresponding error code should be treated as -EFSCORRUPTED.
Signed-off-by: Gao Xiang hsiangkao@linux.alibaba.com
Stable-dep-of: 4012d7856219 ("erofs: fix unexpected EIO under memory pressure")
Signed-off-by: Sasha Levin sashal@kernel.org
---
 fs/erofs/compress.h             |  4 ++--
 fs/erofs/decompressor.c         | 20 +++++++++-----------
 fs/erofs/decompressor_deflate.c | 10 ++++------
 fs/erofs/decompressor_lzma.c    | 10 ++++------
 fs/erofs/decompressor_zstd.c    | 12 ++++--------
 fs/erofs/zdata.c                | 21 +++++++++++++++++----
 6 files changed, 40 insertions(+), 37 deletions(-)

diff --git a/fs/erofs/compress.h b/fs/erofs/compress.h
index 510e922c5193..1ee4ad934c1f 100644
--- a/fs/erofs/compress.h
+++ b/fs/erofs/compress.h
@@ -23,8 +23,8 @@ struct z_erofs_decompress_req {
 struct z_erofs_decompressor {
    int (*config)(struct super_block *sb, struct erofs_super_block *dsb,
    	      void *data, int size);
-	int (*decompress)(struct z_erofs_decompress_req *rq,
-			  struct page **pagepool);
+	const char *(*decompress)(struct z_erofs_decompress_req *rq,
+				  struct page **pagepool);
    int (*init)(void);
    void (*exit)(void);
    char *name;
diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index 354762c9723f..2d6b765dae65 100644
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -228,8 +228,6 @@ static int z_erofs_lz4_decompress_mem(struct z_erofs_decompress_req *rq, u8 *dst
    				  rq->inputsize, rq->outputsize);
if (ret != rq->outputsize) {
-		erofs_err(rq->sb, "failed to decompress %d in[%u, %u] out[%u]",
-			  ret, rq->inputsize, inputmargin, rq->outputsize);
    	if (ret >= 0)
    		memset(out + ret, 0, rq->outputsize - ret);
    	ret = -EFSCORRUPTED;
@@ -250,8 +248,8 @@ static int z_erofs_lz4_decompress_mem(struct z_erofs_decompress_req *rq, u8 *dst
    return ret;
 }
-static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
-				  struct page **pagepool)
+static const char *z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
+					  struct page **pagepool)
 {
    unsigned int dst_maptype;
    void *dst;
@@ -266,14 +264,14 @@ static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
    	/* general decoding path which can be used for all cases */
    	ret = z_erofs_lz4_prepare_dstpages(rq, pagepool);
    	if (ret < 0)
-			return ret;
+			return ERR_PTR(ret);
    	if (ret > 0) {
    		dst = page_address(*rq->out);
    		dst_maptype = 1;
    	} else {
    		dst = erofs_vm_map_ram(rq->out, rq->outpages);
    		if (!dst)
-				return -ENOMEM;
+				return ERR_PTR(-ENOMEM);
    		dst_maptype = 2;
    	}
    }
@@ -282,11 +280,11 @@ static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
    	kunmap_local(dst);
    else if (dst_maptype == 2)
    	vm_unmap_ram(dst, rq->outpages);
-	return ret;
+	return ERR_PTR(ret);
 }
-static int z_erofs_transform_plain(struct z_erofs_decompress_req *rq,
-				   struct page **pagepool)
+static const char *z_erofs_transform_plain(struct z_erofs_decompress_req *rq,
+					   struct page **pagepool)
 {
    const unsigned int nrpages_in = rq->inpages, nrpages_out = rq->outpages;
    const unsigned int bs = rq->sb->s_blocksize;
@@ -294,7 +292,7 @@ static int z_erofs_transform_plain(struct z_erofs_decompress_req *rq,
    u8 *kin;
if (rq->outputsize > rq->inputsize)
-		return -EOPNOTSUPP;
+		return ERR_PTR(-EOPNOTSUPP);
    if (rq->alg == Z_EROFS_COMPRESSION_INTERLACED) {
    	cur = bs - (rq->pageofs_out & (bs - 1));
    	pi = (rq->pageofs_in + rq->inputsize - cur) & ~PAGE_MASK;
@@ -334,7 +332,7 @@ static int z_erofs_transform_plain(struct z_erofs_decompress_req *rq,
    	kunmap_local(kin);
    }
    DBG_BUGON(ni > nrpages_in);
-	return 0;
+	return NULL;
 }
int z_erofs_stream_switch_bufs(struct z_erofs_stream_dctx *dctx, void **dst,
diff --git a/fs/erofs/decompressor_deflate.c b/fs/erofs/decompressor_deflate.c
index 6909b2d529c7..e9c4b740ef89 100644
--- a/fs/erofs/decompressor_deflate.c
+++ b/fs/erofs/decompressor_deflate.c
@@ -157,8 +157,6 @@ static int __z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
    			break;
    		if (zerr == Z_STREAM_END && !rq->outputsize)
    			break;
-			erofs_err(sb, "failed to decompress %d in[%u] out[%u]",
-				  zerr, rq->inputsize, rq->outputsize);
    		err = -EFSCORRUPTED;
    		break;
    	}
@@ -178,8 +176,8 @@ static int __z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
    return err;
 }
-static int z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
-				      struct page **pgpl)
+static const char *z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
+					      struct page **pgpl)
 {
 #ifdef CONFIG_EROFS_FS_ZIP_ACCEL
    int err;
@@ -187,11 +185,11 @@ static int z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
    if (!rq->partial_decoding) {
    	err = z_erofs_crypto_decompress(rq, pgpl);
    	if (err != -EOPNOTSUPP)
-			return err;
+			return ERR_PTR(err);
}
 #endif
-	return __z_erofs_deflate_decompress(rq, pgpl);
+	return ERR_PTR(__z_erofs_deflate_decompress(rq, pgpl));
 }
const struct z_erofs_decompressor z_erofs_deflate_decomp = {
diff --git a/fs/erofs/decompressor_lzma.c b/fs/erofs/decompressor_lzma.c
index 832cffb83a66..7784ced90145 100644
--- a/fs/erofs/decompressor_lzma.c
+++ b/fs/erofs/decompressor_lzma.c
@@ -146,8 +146,8 @@ static int z_erofs_load_lzma_config(struct super_block *sb,
    return err;
 }
-static int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
-				   struct page **pgpl)
+static const char *z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
+					   struct page **pgpl)
 {
    struct super_block *sb = rq->sb;
    struct z_erofs_stream_dctx dctx = { .rq = rq, .no = -1, .ni = 0 };
@@ -162,7 +162,7 @@ static int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
    		min(rq->inputsize, sb->s_blocksize - rq->pageofs_in));
    if (err) {
    	kunmap_local(dctx.kin);
-		return err;
+		return ERR_PTR(err);
    }
/* 2. get an available lzma context */
@@ -207,8 +207,6 @@ static int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
    	if (xz_err != XZ_OK) {
    		if (xz_err == XZ_STREAM_END && !rq->outputsize)
    			break;
-			erofs_err(sb, "failed to decompress %d in[%u] out[%u]",
-				  xz_err, rq->inputsize, rq->outputsize);
    		err = -EFSCORRUPTED;
    		break;
    	}
@@ -223,7 +221,7 @@ static int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
    z_erofs_lzma_head = strm;
    spin_unlock(&z_erofs_lzma_lock);
    wake_up(&z_erofs_lzma_wq);
-	return err;
+	return ERR_PTR(err);
 }
const struct z_erofs_decompressor z_erofs_lzma_decomp = {
diff --git a/fs/erofs/decompressor_zstd.c b/fs/erofs/decompressor_zstd.c
index e38d93bb2104..50fadff89cbc 100644
--- a/fs/erofs/decompressor_zstd.c
+++ b/fs/erofs/decompressor_zstd.c
@@ -135,8 +135,8 @@ static int z_erofs_load_zstd_config(struct super_block *sb,
    return strm ? -ENOMEM : 0;
 }
-static int z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
-				   struct page **pgpl)
+static const char *z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
+					   struct page **pgpl)
 {
    struct super_block *sb = rq->sb;
    struct z_erofs_stream_dctx dctx = { .rq = rq, .no = -1, .ni = 0 };
@@ -152,7 +152,7 @@ static int z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
    		min(rq->inputsize, sb->s_blocksize - rq->pageofs_in));
    if (err) {
    	kunmap_local(dctx.kin);
-		return err;
+		return ERR_PTR(err);
    }
/* 2. get an available ZSTD context */
@@ -191,10 +191,6 @@ static int z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
    	if (zstd_is_error(zerr) ||
    	    ((rq->outputsize + dctx.avail_out) && (!zerr || (zerr > 0 &&
    			!(rq->inputsize + in_buf.size - in_buf.pos))))) {
-			erofs_err(sb, "failed to decompress in[%u] out[%u]: %s",
-				  rq->inputsize, rq->outputsize,
-				  zstd_is_error(zerr) ? zstd_get_error_name(zerr) :
-					"unexpected end of stream");
    		err = -EFSCORRUPTED;
    		break;
    	}
@@ -210,7 +206,7 @@ static int z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
    z_erofs_zstd_head = strm;
    spin_unlock(&z_erofs_zstd_lock);
    wake_up(&z_erofs_zstd_wq);
-	return err;
+	return ERR_PTR(err);
 }
const struct z_erofs_decompressor z_erofs_zstd_decomp = {
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index bc80cfe482f7..461a929e0825 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1267,12 +1267,13 @@ static int z_erofs_decompress_pcluster(struct z_erofs_backend *be, int err)
    struct erofs_sb_info *const sbi = EROFS_SB(be->sb);
    struct z_erofs_pcluster *pcl = be->pcl;
    unsigned int pclusterpages = z_erofs_pclusterpages(pcl);
-	const struct z_erofs_decompressor *decomp =
+	const struct z_erofs_decompressor *alg =
    			z_erofs_decomp[pcl->algorithmformat];
+	bool try_free = true;
    int i, j, jtop, err2;
    struct page *page;
    bool overlapped;
-	bool try_free = true;
+	const char *reason;
mutex_lock(&pcl->lock);
    be->nr_pages = PAGE_ALIGN(pcl->length + pcl->pageofs_out) >> PAGE_SHIFT;
@@ -1304,8 +1305,8 @@ static int z_erofs_decompress_pcluster(struct z_erofs_backend *be, int err)
    err2 = z_erofs_parse_in_bvecs(be, &overlapped);
    if (err2)
    	err = err2;
-	if (!err)
-		err = decomp->decompress(&(struct z_erofs_decompress_req) {
+	if (!err) {
+		reason = alg->decompress(&(struct z_erofs_decompress_req) {
    				.sb = be->sb,
    				.in = be->compressed_pages,
    				.out = be->decompressed_pages,
@@ -1322,6 +1323,18 @@ static int z_erofs_decompress_pcluster(struct z_erofs_backend *be, int err)
    				.gfp = pcl->besteffort ? GFP_KERNEL :
    					GFP_NOWAIT | __GFP_NORETRY
    			 }, be->pagepool);
+		if (IS_ERR(reason)) {
+			erofs_err(be->sb, "failed to decompress (%s) %ld @ pa %llu size %u => %u",
+				  alg->name, PTR_ERR(reason), pcl->pos,
+				  pcl->pclustersize, pcl->length);
+			err = PTR_ERR(reason);
+		} else if (unlikely(reason)) {
+			erofs_err(be->sb, "failed to decompress (%s) %s @ pa %llu size %u => %u",
+				  alg->name, reason, pcl->pos,
+				  pcl->pclustersize, pcl->length);
+			err = -EFSCORRUPTED;
+		}
+	}
/* must handle all compressed pages before actual file pages */
    if (pcl->from_meta) {
-- 
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[PATCH 6.18.y 1/2] erofs: improve decompression error reporting