linux-kernel - Re: [PATCH] zram: return error-valued pointer from zcomp

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Message-Id: <20140305121314.a50e2866c196e2ab983fb910@linux-foundation.org>
Date:	Wed, 5 Mar 2014 12:13:14 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Minchan Kim <minchan@...nel.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] zram: return error-valued pointer from zcomp_create()

On Wed,  5 Mar 2014 22:56:55 +0300 Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:

> Instead of returning just NULL, return ERR_PTR from zcomp_create()
> if compressing backend creation has failed. ERR_PTR(-EINVAL) for
> unsupported compression algorithm request, ERR_PTR(-ENOMEM) for
> allocation (zcomp or compression stream) error.
> 
> Perform IS_ERR() check of returned from zcomp_create() value in
> disksize_store() and set return code to PTR_ERR().
> 
> Change suggested by Jerome Marchand.
> 
> ...
>
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -583,7 +583,7 @@ static ssize_t disksize_store(struct device *dev,
>  	struct zcomp *comp;
>  	struct zram_meta *meta;
>  	struct zram *zram = dev_to_zram(dev);
> -	int err = -EINVAL;
> +	int err = -EBUSY;
>  
>  	disksize = memparse(buf, NULL);
>  	if (!disksize)
> @@ -595,9 +595,10 @@ static ssize_t disksize_store(struct device *dev,
>  		return -ENOMEM;
>  
>  	comp = zcomp_create(zram->compressor, zram->max_comp_streams);
> -	if (!comp) {
> +	if (IS_ERR(comp)) {
>  		pr_info("Cannot initialise %s compressing backend\n",
>  				zram->compressor);
> +		err = PTR_ERR(comp);
>  		goto out_cleanup;
>  	}
>  
> @@ -605,7 +606,6 @@ static ssize_t disksize_store(struct device *dev,
>  	if (init_done(zram)) {
>  		up_write(&zram->init_lock);
>  		pr_info("Cannot change disksize for initialized device\n");
> -		err = -EBUSY;
>  		goto out_cleanup;
>  	}
>  
> @@ -618,7 +618,7 @@ static ssize_t disksize_store(struct device *dev,
>  	return len;
>  
>  out_cleanup:
> -	if (comp)
> +	if (!IS_ERR(comp))
>  		zcomp_destroy(comp);
>  	zram_meta_free(meta);
>  	return err;

The disksize_store() error ends up being unnecessarily inconsistent in
its handling of `err' and in its freeing/unlocking flow.  How about
doing it this way?

static ssize_t disksize_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t len)
{
	u64 disksize;
	struct zcomp *comp;
	struct zram_meta *meta;
	struct zram *zram = dev_to_zram(dev);
	int err;

	disksize = memparse(buf, NULL);
	if (!disksize)
		return -EINVAL;

	disksize = PAGE_ALIGN(disksize);
	meta = zram_meta_alloc(disksize);
	if (!meta)
		return -ENOMEM;

	comp = zcomp_create(zram->compressor, zram->max_comp_streams);
	if (IS_ERR(comp)) {
		pr_info("Cannot initialise %s compressing backend\n",
				zram->compressor);
		err = PTR_ERR(comp);
		goto out_free_meta;
	}

	down_write(&zram->init_lock);
	if (init_done(zram)) {
		pr_info("Cannot change disksize for initialized device\n");
		err = -EBUSY;
		goto out_destroy_comp;
	}

	zram->meta = meta;
	zram->comp = comp;
	zram->disksize = disksize;
	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
	up_write(&zram->init_lock);
	return len;

out_destroy_comp:
	up_write(&zram->init_lock);
	zcomp_destroy(comp);
out_free_meta:
	zram_meta_free(meta);
	return err;
}

--- a/drivers/block/zram/zram_drv.c~zram-return-error-valued-pointer-from-zcomp_create-fix
+++ a/drivers/block/zram/zram_drv.c
@@ -583,7 +583,7 @@ static ssize_t disksize_store(struct dev
 	struct zcomp *comp;
 	struct zram_meta *meta;
 	struct zram *zram = dev_to_zram(dev);
-	int err = -EBUSY;
+	int err;
 
 	disksize = memparse(buf, NULL);
 	if (!disksize)
@@ -599,14 +599,14 @@ static ssize_t disksize_store(struct dev
 		pr_info("Cannot initialise %s compressing backend\n",
 				zram->compressor);
 		err = PTR_ERR(comp);
-		goto out_cleanup;
+		goto out_free_meta;
 	}
 
 	down_write(&zram->init_lock);
 	if (init_done(zram)) {
-		up_write(&zram->init_lock);
 		pr_info("Cannot change disksize for initialized device\n");
-		goto out_cleanup;
+		err = -EBUSY;
+		goto out_destroy_comp;
 	}
 
 	zram->meta = meta;
@@ -617,9 +617,10 @@ static ssize_t disksize_store(struct dev
 
 	return len;
 
-out_cleanup:
-	if (!IS_ERR(comp))
-		zcomp_destroy(comp);
+out_destroy_comp:
+	up_write(&zram->init_lock);
+	zcomp_destroy(comp);
+out_free_meta:
 	zram_meta_free(meta);
 	return err;
 }
_


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