linux-kernel - Re: [PATCH] jffs2: reduce stack usage in jffs2_build_xattr

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Message-ID: <e6f4327a-83f0-22dc-e186-9012912b25d9@huawei.com>
Date:   Sat, 6 May 2023 21:11:15 +0800
From:   Zhihao Cheng <chengzhihao1@...wei.com>
To:     Christian Marangi <ansuelsmth@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Richard Weinberger <richard@....at>,
        Fabian Frederick <fabf@...net.be>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Christian Brauner <brauner@...nel.org>,
        KaiGai Kohei <kaigai@...jp.nec.com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
CC:     Tim Gardner <tim.gardner@...onical.com>,
        kernel test robot <lkp@...el.com>,
        Ron Economos <re@...z.net>,
        Nathan Chancellor <nathan@...nel.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH] jffs2: reduce stack usage in
 jffs2_build_xattr_subsystem()

在 2023/5/6 12:56, Christian Marangi 写道:
> From: Fabian Frederick <fabf@...net.be>
> 
> Use kcalloc() for allocation/flush of 128 pointers table to
> reduce stack usage.
> 
> Function now returns -ENOMEM or 0 on success.
> 
> stackusage
> Before:
> ./fs/jffs2/xattr.c:775  jffs2_build_xattr_subsystem     1208
> dynamic,bounded
> 
> After:
> ./fs/jffs2/xattr.c:775  jffs2_build_xattr_subsystem     192
> dynamic,bounded
> 
> Also update definition when CONFIG_JFFS2_FS_XATTR is not enabled
> 
> Tested with an MTD mount point and some user set/getfattr.
> 
> Many current target on OpenWRT also suffer from a compilation warning
> (that become an error with CONFIG_WERROR) with the following output:
> 
> fs/jffs2/xattr.c: In function 'jffs2_build_xattr_subsystem':
> fs/jffs2/xattr.c:887:1: error: the frame size of 1088 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
>    887 | }
>        | ^
> 
> Using dynamic allocation fix this compilation warning.
> 
> Fixes: c9f700f840bd ("[JFFS2][XATTR] using 'delete marker' for xdatum/xref deletion")
> Reported-by: Tim Gardner <tim.gardner@...onical.com>
> Reported-by: kernel test robot <lkp@...el.com>
> Reported-by: Ron Economos <re@...z.net>
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Fabian Frederick <fabf@...net.be>
> Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
> Cc: stable@...r.kernel.org
> ---
>   fs/jffs2/build.c |  5 ++++-
>   fs/jffs2/xattr.c | 13 +++++++++----
>   fs/jffs2/xattr.h |  4 ++--
>   3 files changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/jffs2/build.c b/fs/jffs2/build.c
> index 837cd55fd4c5..6ae9d6fefb86 100644
> --- a/fs/jffs2/build.c
> +++ b/fs/jffs2/build.c
> @@ -211,7 +211,10 @@ static int jffs2_build_filesystem(struct jffs2_sb_info *c)
>   		ic->scan_dents = NULL;
>   		cond_resched();
>   	}
> -	jffs2_build_xattr_subsystem(c);
> +	ret = jffs2_build_xattr_subsystem(c);
> +	if (ret)
> +		goto exit;
> +
>   	c->flags &= ~JFFS2_SB_FLAG_BUILDING;
>   
>   	dbg_fsbuild("FS build complete\n");
> diff --git a/fs/jffs2/xattr.c b/fs/jffs2/xattr.c
> index aa4048a27f31..3b6bdc9a49e1 100644
> --- a/fs/jffs2/xattr.c
> +++ b/fs/jffs2/xattr.c
> @@ -772,10 +772,10 @@ void jffs2_clear_xattr_subsystem(struct jffs2_sb_info *c)
>   }
>   
>   #define XREF_TMPHASH_SIZE	(128)
> -void jffs2_build_xattr_subsystem(struct jffs2_sb_info *c)
> +int jffs2_build_xattr_subsystem(struct jffs2_sb_info *c)
>   {
>   	struct jffs2_xattr_ref *ref, *_ref;
> -	struct jffs2_xattr_ref *xref_tmphash[XREF_TMPHASH_SIZE];
> +	struct jffs2_xattr_ref **xref_tmphash;
>   	struct jffs2_xattr_datum *xd, *_xd;
>   	struct jffs2_inode_cache *ic;
>   	struct jffs2_raw_node_ref *raw;
> @@ -784,9 +784,12 @@ void jffs2_build_xattr_subsystem(struct jffs2_sb_info *c)
>   
>   	BUG_ON(!(c->flags & JFFS2_SB_FLAG_BUILDING));
>   
> +	xref_tmphash = kcalloc(XREF_TMPHASH_SIZE,
> +			       sizeof(struct jffs2_xattr_ref *), GFP_KERNEL);
> +	if (!xref_tmphash)
> +		return -ENOMEM;
> +

I have made some fault injection tests, jffs2 works fine, this patch 
imports no memleak problems. It seems okay.

>   	/* Phase.1 : Merge same xref */
> -	for (i=0; i < XREF_TMPHASH_SIZE; i++)
> -		xref_tmphash[i] = NULL;
>   	for (ref=c->xref_temp; ref; ref=_ref) {
>   		struct jffs2_xattr_ref *tmp;
>   
> @@ -884,6 +887,8 @@ void jffs2_build_xattr_subsystem(struct jffs2_sb_info *c)
>   		     "%u of xref (%u dead, %u orphan) found.\n",
>   		     xdatum_count, xdatum_unchecked_count, xdatum_orphan_count,
>   		     xref_count, xref_dead_count, xref_orphan_count);
> +	kfree(xref_tmphash);
> +	return 0;
>   }
>   
>   struct jffs2_xattr_datum *jffs2_setup_xattr_datum(struct jffs2_sb_info *c,
> diff --git a/fs/jffs2/xattr.h b/fs/jffs2/xattr.h
> index 720007b2fd65..1b5030a3349d 100644
> --- a/fs/jffs2/xattr.h
> +++ b/fs/jffs2/xattr.h
> @@ -71,7 +71,7 @@ static inline int is_xattr_ref_dead(struct jffs2_xattr_ref *ref)
>   #ifdef CONFIG_JFFS2_FS_XATTR
>   
>   extern void jffs2_init_xattr_subsystem(struct jffs2_sb_info *c);
> -extern void jffs2_build_xattr_subsystem(struct jffs2_sb_info *c);
> +extern int jffs2_build_xattr_subsystem(struct jffs2_sb_info *c);
>   extern void jffs2_clear_xattr_subsystem(struct jffs2_sb_info *c);
>   
>   extern struct jffs2_xattr_datum *jffs2_setup_xattr_datum(struct jffs2_sb_info *c,
> @@ -103,7 +103,7 @@ extern ssize_t jffs2_listxattr(struct dentry *, char *, size_t);
>   #else
>   
>   #define jffs2_init_xattr_subsystem(c)
> -#define jffs2_build_xattr_subsystem(c)
> +#define jffs2_build_xattr_subsystem(c)		(0)
>   #define jffs2_clear_xattr_subsystem(c)
>   
>   #define jffs2_xattr_do_crccheck_inode(c, ic)
>