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

[Nick Desaulniers <ndesaulniers@google.com>]

On Tue, May 09, 2017 at 10:30:03PM +0200, Fabian Frederick wrote:
> 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.
> 
> Signed-off-by: Fabian Frederick <fabf@skynet.be>

Hi David,
Any chance this patch can get picked up? It LGTM, and I see multiple
reports of this issue on lore:
https://lore.kernel.org/lkml/?q=jffs2_build_xattr_subsystem

Reported-by: Tim Gardner <tim.gardner@canonical.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Ron Economos <re@w6rz.net>
Reported-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  fs/jffs2/build.c |  5 ++++-
>  fs/jffs2/xattr.c | 14 ++++++++++----
>  fs/jffs2/xattr.h |  4 ++--
>  3 files changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/jffs2/build.c b/fs/jffs2/build.c
> index b288c8a..f88e0bf 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 da3e185..95c0496 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 +784,13 @@ 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;
> +
>  	/* 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 +888,8 @@ 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 720007b..1b5030a 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)
> -- 
> 2.9.3
>