Re: [PATCH] jffs2: reduce stack usage in jffs2_build_xattr_subsystem()

[Zhihao Cheng]

在 2023/5/6 12:56, Christian Marangi 写道:
> From: Fabian Frederick <fabf@xxxxxxxxx>
>
> 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@xxxxxxxxxxxxx>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Reported-by: Ron Economos <re@xxxxxxxx>
> Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Signed-off-by: Fabian Frederick <fabf@xxxxxxxxx>
> Signed-off-by: Christian Marangi <ansuelsmth@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
>   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)