+ zram-check-that-backends-array-has-at-least-one-backend.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: zram: check that backends array has at least one backend
has been added to the -mm mm-unstable branch.  Its filename is
     zram-check-that-backends-array-has-at-least-one-backend.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-check-that-backends-array-has-at-least-one-backend.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Sergey Senozhatsky <senozhatsky@chromium.org>
Subject: zram: check that backends array has at least one backend
Date: Fri, 12 Jul 2024 14:18:23 +0900

Make sure that backends array has anything apart from the
sentinel NULL value.

We also select LZO_BACKEND if none backends were selected.

Link: https://lkml.kernel.org/r/20240712051850.484318-13-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nick Terrell <terrelln@fb.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/block/zram/Kconfig |   19 +++++++++++++------
 drivers/block/zram/zcomp.c |    8 ++++++++
 2 files changed, 21 insertions(+), 6 deletions(-)

--- a/drivers/block/zram/Kconfig~zram-check-that-backends-array-has-at-least-one-backend
+++ a/drivers/block/zram/Kconfig
@@ -15,12 +15,6 @@ config ZRAM
 
 	  See Documentation/admin-guide/blockdev/zram.rst for more information.
 
-config ZRAM_BACKEND_LZO
-	bool "lzo and lzo-rle compression support"
-	depends on ZRAM
-	select LZO_COMPRESS
-	select LZO_DECOMPRESS
-
 config ZRAM_BACKEND_LZ4
 	bool "lz4 compression support"
 	depends on ZRAM
@@ -51,6 +45,19 @@ config ZRAM_BACKEND_842
 	select 842_COMPRESS
 	select 842_DECOMPRESS
 
+config ZRAM_BACKEND_FORCE_LZO
+	depends on ZRAM
+	def_bool !ZRAM_BACKEND_LZ4 && !ZRAM_BACKEND_LZ4HC && \
+		!ZRAM_BACKEND_ZSTD && !ZRAM_BACKEND_DEFLATE && \
+		!ZRAM_BACKEND_842
+
+config ZRAM_BACKEND_LZO
+	bool "lzo and lzo-rle compression support" if !ZRAM_BACKEND_FORCE_LZO
+	depends on ZRAM
+	default ZRAM_BACKEND_FORCE_LZO
+	select LZO_COMPRESS
+	select LZO_DECOMPRESS
+
 choice
 	prompt "Default zram compressor"
 	default ZRAM_DEF_COMP_LZORLE
--- a/drivers/block/zram/zcomp.c~zram-check-that-backends-array-has-at-least-one-backend
+++ a/drivers/block/zram/zcomp.c
@@ -191,6 +191,14 @@ struct zcomp *zcomp_create(const char *a
 	struct zcomp *comp;
 	int error;
 
+	/*
+	 * The backends array has a sentinel NULL value, so the minimum
+	 * size is 1. In order to be valid the array, apart from the
+	 * sentinel NULL element, should have at least one compression
+	 * backend selected.
+	 */
+	BUILD_BUG_ON(ARRAY_SIZE(backends) <= 1);
+
 	comp = kzalloc(sizeof(struct zcomp), GFP_KERNEL);
 	if (!comp)
 		return ERR_PTR(-ENOMEM);
_

Patches currently in -mm which might be from senozhatsky@chromium.org are

lib-zstd-export-api-needed-for-dictionary-support.patch
lib-lz4hc-export-lz4_resetstreamhc-symbol.patch
lib-zstd-fix-null-deref-in-zstd_createcdict_advanced2.patch
zram-introduce-custom-comp-backends-api.patch
zram-add-lzo-and-lzorle-compression-backends-support.patch
zram-add-lz4-compression-backend-support.patch
zram-add-lz4hc-compression-backend-support.patch
zram-add-zstd-compression-backend-support.patch
zram-pass-estimated-src-size-hint-to-zstd.patch
zram-add-zlib-compression-backend-support.patch
zram-add-842-compression-backend-support.patch
zram-check-that-backends-array-has-at-least-one-backend.patch
zram-introduce-zcomp_params-structure.patch
zram-recalculate-zstd-compression-params-once.patch
zram-extend-comp_algorithm-attr-write-handling.patch
zram-add-support-for-dict-comp-config.patch
zram-introduce-zcomp_req-structure.patch
zram-introduce-zcomp_ctx-structure.patch
zram-move-immutable-comp-params-away-from-per-cpu-context.patch
zram-add-dictionary-support-to-lz4.patch
zram-add-dictionary-support-to-lz4hc.patch
zram-add-dictionary-support-to-zstd-backend.patch
documentation-zram-add-documentation-for-algorithm-parameters.patch