lib: Revert use of fallthrough pseudo-keyword in lib/

The following build error for powerpc64 was reported by Nathan Chancellor:

  "$ scripts/config --file arch/powerpc/configs/powernv_defconfig -e KERNEL_XZ

   $ make -skj"$(nproc)" ARCH=powerpc CROSS_COMPILE=powerpc64le-linux- distclean powernv_defconfig zImage
   ...
   In file included from arch/powerpc/boot/../../../lib/decompress_unxz.c:234,
                    from arch/powerpc/boot/decompress.c:38:
   arch/powerpc/boot/../../../lib/xz/xz_dec_stream.c: In function 'dec_main':
   arch/powerpc/boot/../../../lib/xz/xz_dec_stream.c:586:4: error: 'fallthrough' undeclared (first use in this function)
     586 |    fallthrough;
         |    ^~~~~~~~~~~

   This will end up affecting distribution configurations such as Debian
   and OpenSUSE according to my testing. I am not sure what the solution
   is, the PowerPC wrapper does not set -D__KERNEL__ so I am not sure
   that compiler_attributes.h can be safely included."

In order to avoid these sort of problems, it seems that the best
solution is to use /* fall through */ comments instead of the
fallthrough pseudo-keyword macro in lib/, for now.

Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Fixes: df561f6688fe ("treewide: Use fallthrough pseudo-keyword")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-and-tested-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 14 insertions, 14 deletions

diff --git a/lib/zstd/bitstream.h b/lib/zstd/bitstream.h
index 7c65c66e41fd..3a49784d5c61 100644
--- a/lib/zstd/bitstream.h
+++ b/lib/zstd/bitstream.h
@@ -259,15 +259,15 @@ ZSTD_STATIC size_t BIT_initDStream(BIT_DStream_t *bitD, const void *srcBuffer, s
 		bitD->bitContainer = *(const BYTE *)(bitD->start);
 		switch (srcSize) {
 		case 7: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[6]) << (sizeof(bitD->bitContainer) * 8 - 16);
-			fallthrough;
+			/* fall through */
 		case 6: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[5]) << (sizeof(bitD->bitContainer) * 8 - 24);
-			fallthrough;
+			/* fall through */
 		case 5: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[4]) << (sizeof(bitD->bitContainer) * 8 - 32);
-			fallthrough;
+			/* fall through */
 		case 4: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[3]) << 24;
-			fallthrough;
+			/* fall through */
 		case 3: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[2]) << 16;
-			fallthrough;
+			/* fall through */
 		case 2: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[1]) << 8;
 		default:;
 		}
diff --git a/lib/zstd/compress.c b/lib/zstd/compress.c
index b080264ed3ad..5e0b67003e55 100644
--- a/lib/zstd/compress.c
+++ b/lib/zstd/compress.c
@@ -3182,7 +3182,7 @@ static size_t ZSTD_compressStream_generic(ZSTD_CStream *zcs, void *dst, size_t *
 				zcs->outBuffFlushedSize = 0;
 				zcs->stage = zcss_flush; /* pass-through to flush stage */
 			}
-			fallthrough;
+			/* fall through */
 
 		case zcss_flush: {
 			size_t const toFlush = zcs->outBuffContentSize - zcs->outBuffFlushedSize;
diff --git a/lib/zstd/decompress.c b/lib/zstd/decompress.c
index 66cd487a326a..db6761ea4deb 100644
--- a/lib/zstd/decompress.c
+++ b/lib/zstd/decompress.c
@@ -442,7 +442,7 @@ size_t ZSTD_decodeLiteralsBlock(ZSTD_DCtx *dctx, const void *src, size_t srcSize
 		case set_repeat:
 			if (dctx->litEntropy == 0)
 				return ERROR(dictionary_corrupted);
-			fallthrough;
+			/* fall through */
 		case set_compressed:
 			if (srcSize < 5)
 				return ERROR(corruption_detected); /* srcSize >= MIN_CBLOCK_SIZE == 3; here we need up to 5 for case 3 */
@@ -1768,7 +1768,7 @@ size_t ZSTD_decompressContinue(ZSTD_DCtx *dctx, void *dst, size_t dstCapacity, c
 			return 0;
 		}
 		dctx->expected = 0; /* not necessary to copy more */
-		fallthrough;
+		/* fall through */
 
 	case ZSTDds_decodeFrameHeader:
 		memcpy(dctx->headerBuffer + ZSTD_frameHeaderSize_prefix, src, dctx->expected);
@@ -2309,7 +2309,7 @@ size_t ZSTD_decompressStream(ZSTD_DStream *zds, ZSTD_outBuffer *output, ZSTD_inB
 		switch (zds->stage) {
 		case zdss_init:
 			ZSTD_resetDStream(zds); /* transparent reset on starting decoding a new frame */
-			fallthrough;
+			/* fall through */
 
 		case zdss_loadHeader: {
 			size_t const hSize = ZSTD_getFrameParams(&zds->fParams, zds->headerBuffer, zds->lhSize);
@@ -2376,7 +2376,7 @@ size_t ZSTD_decompressStream(ZSTD_DStream *zds, ZSTD_outBuffer *output, ZSTD_inB
 			}
 			zds->stage = zdss_read;
 		}
-			fallthrough;
+			/* fall through */
 
 		case zdss_read: {
 			size_t const neededInSize = ZSTD_nextSrcSizeToDecompress(zds->dctx);
@@ -2405,7 +2405,7 @@ size_t ZSTD_decompressStream(ZSTD_DStream *zds, ZSTD_outBuffer *output, ZSTD_inB
 			zds->stage = zdss_load;
 			/* pass-through */
 		}
-			fallthrough;
+			/* fall through */
 
 		case zdss_load: {
 			size_t const neededInSize = ZSTD_nextSrcSizeToDecompress(zds->dctx);
@@ -2438,7 +2438,7 @@ size_t ZSTD_decompressStream(ZSTD_DStream *zds, ZSTD_outBuffer *output, ZSTD_inB
 				/* pass-through */
 			}
 		}
-			fallthrough;
+			/* fall through */
 
 		case zdss_flush: {
 			size_t const toFlushSize = zds->outEnd - zds->outStart;
diff --git a/lib/zstd/huf_compress.c b/lib/zstd/huf_compress.c
index 08b4ae80aed4..e727812d12aa 100644
--- a/lib/zstd/huf_compress.c
+++ b/lib/zstd/huf_compress.c
@@ -556,9 +556,9 @@ size_t HUF_compress1X_usingCTable(void *dst, size_t dstSize, const void *src, si
 	n = srcSize & ~3; /* join to mod 4 */
 	switch (srcSize & 3) {
 	case 3: HUF_encodeSymbol(&bitC, ip[n + 2], CTable); HUF_FLUSHBITS_2(&bitC);
-		fallthrough;
+		/* fall through */
 	case 2: HUF_encodeSymbol(&bitC, ip[n + 1], CTable); HUF_FLUSHBITS_1(&bitC);
-		fallthrough;
+		/* fall through */
 	case 1: HUF_encodeSymbol(&bitC, ip[n + 0], CTable); HUF_FLUSHBITS(&bitC);
 	case 0:
 	default:;