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[PATCHv2] mm/zsmalloc: don't fail if can't create debugfs info

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  [PATCHv2] mm/zsmalloc: don't fail if can't create debugfs info Dan Streetman <ddstreet@ieee.org> - 2016-05-19 17:30 +0200
    Re: [PATCHv2] mm/zsmalloc: don't fail if can't create debugfs info Ganesh Mahendran <opensource.ganesh@gmail.com> - 2016-05-20 04:40 +0200
    Re: [PATCHv2] mm/zsmalloc: don't fail if can't create debugfs info Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-05-20 06:10 +0200
      Re: [PATCHv2] mm/zsmalloc: don't fail if can't create debugfs info Dan Streetman <ddstreet@ieee.org> - 2016-05-20 12:40 +0200
    Re: [PATCHv2] mm/zsmalloc: don't fail if can't create debugfs info Minchan Kim <minchan@kernel.org> - 2016-05-23 05:10 +0200

#1403812 — [PATCHv2] mm/zsmalloc: don't fail if can't create debugfs info

Change the return type of zs_pool_stat_create() to void, and
remove the logic to abort pool creation if the stat debugfs
dir/file could not be created.

The debugfs stat file is for debugging/information only, and doesn't
affect operation of zsmalloc; there is no reason to abort creating
the pool if the stat file can't be created.  This was seen with
zswap, which used the same name for all pool creations, which caused
zsmalloc to fail to create a second pool for zswap if
CONFIG_ZSMALLOC_STAT was enabled.

Signed-off-by: Dan Streetman <ddstreet@ieee.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Dan Streetman <dan.streetman@canonical.com>
Cc: Minchan Kim <minchan@kernel.org>

---
Changes since v1:
 -add pr_warn to all stat failure cases
 -do not prevent module loading on stat failure

 mm/zsmalloc.c | 51 ++++++++++++++++++++++-----------------------------
 1 file changed, 22 insertions(+), 29 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index aba39a2..b6d4f25 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -45,6 +45,8 @@
  *
  */
 
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/sched.h>
@@ -483,16 +485,16 @@ static inline unsigned long zs_stat_get(struct size_class *class,
 
 #ifdef CONFIG_ZSMALLOC_STAT
 
-static int __init zs_stat_init(void)
+static void __init zs_stat_init(void)
 {
-	if (!debugfs_initialized())
-		return -ENODEV;
+	if (!debugfs_initialized()) {
+		pr_warn("debugfs not available, stat dir not created\n");
+		return;
+	}
 
 	zs_stat_root = debugfs_create_dir("zsmalloc", NULL);
 	if (!zs_stat_root)
-		return -ENOMEM;
-
-	return 0;
+		pr_warn("debugfs 'zsmalloc' stat dir creation failed\n");
 }
 
 static void __exit zs_stat_exit(void)
@@ -573,17 +575,19 @@ static const struct file_operations zs_stat_size_ops = {
 	.release        = single_release,
 };
 
-static int zs_pool_stat_create(struct zs_pool *pool, const char *name)
+static void zs_pool_stat_create(struct zs_pool *pool, const char *name)
 {
 	struct dentry *entry;
 
-	if (!zs_stat_root)
-		return -ENODEV;
+	if (!zs_stat_root) {
+		pr_warn("no root stat dir, not creating <%s> stat dir\n", name);
+		return;
+	}
 
 	entry = debugfs_create_dir(name, zs_stat_root);
 	if (!entry) {
 		pr_warn("debugfs dir <%s> creation failed\n", name);
-		return -ENOMEM;
+		return;
 	}
 	pool->stat_dentry = entry;
 
@@ -592,10 +596,9 @@ static int zs_pool_stat_create(struct zs_pool *pool, const char *name)
 	if (!entry) {
 		pr_warn("%s: debugfs file entry <%s> creation failed\n",
 				name, "classes");
-		return -ENOMEM;
+		debugfs_remove_recursive(pool->stat_dentry);
+		pool->stat_dentry = NULL;
 	}
-
-	return 0;
 }
 
 static void zs_pool_stat_destroy(struct zs_pool *pool)
@@ -604,18 +607,16 @@ static void zs_pool_stat_destroy(struct zs_pool *pool)
 }
 
 #else /* CONFIG_ZSMALLOC_STAT */
-static int __init zs_stat_init(void)
+static void __init zs_stat_init(void)
 {
-	return 0;
 }
 
 static void __exit zs_stat_exit(void)
 {
 }
 
-static inline int zs_pool_stat_create(struct zs_pool *pool, const char *name)
+static inline void zs_pool_stat_create(struct zs_pool *pool, const char *name)
 {
-	return 0;
 }
 
 static inline void zs_pool_stat_destroy(struct zs_pool *pool)
@@ -623,7 +624,6 @@ static inline void zs_pool_stat_destroy(struct zs_pool *pool)
 }
 #endif
 
-
 /*
  * For each size class, zspages are divided into different groups
  * depending on how "full" they are. This was done so that we could
@@ -1952,8 +1952,8 @@ struct zs_pool *zs_create_pool(const char *name)
 		prev_class = class;
 	}
 
-	if (zs_pool_stat_create(pool, name))
-		goto err;
+	/* debug only, don't abort if it fails */
+	zs_pool_stat_create(pool, name);
 
 	/*
 	 * Not critical, we still can use the pool
@@ -2015,17 +2015,10 @@ static int __init zs_init(void)
 	zpool_register_driver(&zs_zpool_driver);
 #endif
 
-	ret = zs_stat_init();
-	if (ret) {
-		pr_err("zs stat initialization failed\n");
-		goto stat_fail;
-	}
+	zs_stat_init();
+
 	return 0;
 
-stat_fail:
-#ifdef CONFIG_ZPOOL
-	zpool_unregister_driver(&zs_zpool_driver);
-#endif
 notifier_fail:
 	zs_unregister_cpu_notifier();
 
-- 
2.7.4

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#1404079

2016-05-19 23:18 GMT+08:00 Dan Streetman <ddstreet@ieee.org>:
> Change the return type of zs_pool_stat_create() to void, and
> remove the logic to abort pool creation if the stat debugfs
> dir/file could not be created.
>
> The debugfs stat file is for debugging/information only, and doesn't
> affect operation of zsmalloc; there is no reason to abort creating
> the pool if the stat file can't be created.  This was seen with
> zswap, which used the same name for all pool creations, which caused
> zsmalloc to fail to create a second pool for zswap if
> CONFIG_ZSMALLOC_STAT was enabled.
>
> Signed-off-by: Dan Streetman <ddstreet@ieee.org>
> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> Cc: Dan Streetman <dan.streetman@canonical.com>
> Cc: Minchan Kim <minchan@kernel.org>
>
> ---
> Changes since v1:
>  -add pr_warn to all stat failure cases
>  -do not prevent module loading on stat failure
>

Reviewed-by: Ganesh Mahendran <opensource.ganesh@gmail.com>

>  mm/zsmalloc.c | 51 ++++++++++++++++++++++-----------------------------
>  1 file changed, 22 insertions(+), 29 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index aba39a2..b6d4f25 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -45,6 +45,8 @@
>   *
>   */
>
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
>  #include <linux/module.h>
>  #include <linux/kernel.h>
>  #include <linux/sched.h>
> @@ -483,16 +485,16 @@ static inline unsigned long zs_stat_get(struct size_class *class,
>
>  #ifdef CONFIG_ZSMALLOC_STAT
>
> -static int __init zs_stat_init(void)
> +static void __init zs_stat_init(void)
>  {
> -       if (!debugfs_initialized())
> -               return -ENODEV;
> +       if (!debugfs_initialized()) {
> +               pr_warn("debugfs not available, stat dir not created\n");
> +               return;
> +       }
>
>         zs_stat_root = debugfs_create_dir("zsmalloc", NULL);
>         if (!zs_stat_root)
> -               return -ENOMEM;
> -
> -       return 0;
> +               pr_warn("debugfs 'zsmalloc' stat dir creation failed\n");
>  }
>
>  static void __exit zs_stat_exit(void)
> @@ -573,17 +575,19 @@ static const struct file_operations zs_stat_size_ops = {
>         .release        = single_release,
>  };
>
> -static int zs_pool_stat_create(struct zs_pool *pool, const char *name)
> +static void zs_pool_stat_create(struct zs_pool *pool, const char *name)
>  {
>         struct dentry *entry;
>
> -       if (!zs_stat_root)
> -               return -ENODEV;
> +       if (!zs_stat_root) {
> +               pr_warn("no root stat dir, not creating <%s> stat dir\n", name);
> +               return;
> +       }
>
>         entry = debugfs_create_dir(name, zs_stat_root);
>         if (!entry) {
>                 pr_warn("debugfs dir <%s> creation failed\n", name);
> -               return -ENOMEM;
> +               return;
>         }
>         pool->stat_dentry = entry;
>
> @@ -592,10 +596,9 @@ static int zs_pool_stat_create(struct zs_pool *pool, const char *name)
>         if (!entry) {
>                 pr_warn("%s: debugfs file entry <%s> creation failed\n",
>                                 name, "classes");
> -               return -ENOMEM;
> +               debugfs_remove_recursive(pool->stat_dentry);
> +               pool->stat_dentry = NULL;
>         }
> -
> -       return 0;
>  }
>
>  static void zs_pool_stat_destroy(struct zs_pool *pool)
> @@ -604,18 +607,16 @@ static void zs_pool_stat_destroy(struct zs_pool *pool)
>  }
>
>  #else /* CONFIG_ZSMALLOC_STAT */
> -static int __init zs_stat_init(void)
> +static void __init zs_stat_init(void)
>  {
> -       return 0;
>  }
>
>  static void __exit zs_stat_exit(void)
>  {
>  }
>
> -static inline int zs_pool_stat_create(struct zs_pool *pool, const char *name)
> +static inline void zs_pool_stat_create(struct zs_pool *pool, const char *name)
>  {
> -       return 0;
>  }
>
>  static inline void zs_pool_stat_destroy(struct zs_pool *pool)
> @@ -623,7 +624,6 @@ static inline void zs_pool_stat_destroy(struct zs_pool *pool)
>  }
>  #endif
>
> -
>  /*
>   * For each size class, zspages are divided into different groups
>   * depending on how "full" they are. This was done so that we could
> @@ -1952,8 +1952,8 @@ struct zs_pool *zs_create_pool(const char *name)
>                 prev_class = class;
>         }
>
> -       if (zs_pool_stat_create(pool, name))
> -               goto err;
> +       /* debug only, don't abort if it fails */
> +       zs_pool_stat_create(pool, name);
>
>         /*
>          * Not critical, we still can use the pool
> @@ -2015,17 +2015,10 @@ static int __init zs_init(void)
>         zpool_register_driver(&zs_zpool_driver);
>  #endif
>
> -       ret = zs_stat_init();
> -       if (ret) {
> -               pr_err("zs stat initialization failed\n");
> -               goto stat_fail;
> -       }
> +       zs_stat_init();
> +
>         return 0;
>
> -stat_fail:
> -#ifdef CONFIG_ZPOOL
> -       zpool_unregister_driver(&zs_zpool_driver);
> -#endif
>  notifier_fail:
>         zs_unregister_cpu_notifier();
>
> --
> 2.7.4
>

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#1404119

On (05/19/16 11:18), Dan Streetman wrote:
[..]
>  	zs_stat_root = debugfs_create_dir("zsmalloc", NULL);
>  	if (!zs_stat_root)
> -		return -ENOMEM;
> -
> -	return 0;
> +		pr_warn("debugfs 'zsmalloc' stat dir creation failed\n");
>  }
>  
>  static void __exit zs_stat_exit(void)
> @@ -573,17 +575,19 @@ static const struct file_operations zs_stat_size_ops = {
>  	.release        = single_release,
>  };
>  
> -static int zs_pool_stat_create(struct zs_pool *pool, const char *name)
> +static void zs_pool_stat_create(struct zs_pool *pool, const char *name)
>  {
>  	struct dentry *entry;
>  
> -	if (!zs_stat_root)
> -		return -ENODEV;
> +	if (!zs_stat_root) {
> +		pr_warn("no root stat dir, not creating <%s> stat dir\n", name);
> +		return;
> +	}

just a small nit, there are basically two warn messages now for
`!zs_stat_root':

	debugfs 'zsmalloc' stat dir creation failed
	no root stat dir, not creating <%s> stat dir

may be we need only one of them; but no strong opinions.

	-ss

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#1404334

On Fri, May 20, 2016 at 12:08 AM, Sergey Senozhatsky
<sergey.senozhatsky.work@gmail.com> wrote:
> On (05/19/16 11:18), Dan Streetman wrote:
> [..]
>>       zs_stat_root = debugfs_create_dir("zsmalloc", NULL);
>>       if (!zs_stat_root)
>> -             return -ENOMEM;
>> -
>> -     return 0;
>> +             pr_warn("debugfs 'zsmalloc' stat dir creation failed\n");
>>  }
>>
>>  static void __exit zs_stat_exit(void)
>> @@ -573,17 +575,19 @@ static const struct file_operations zs_stat_size_ops = {
>>       .release        = single_release,
>>  };
>>
>> -static int zs_pool_stat_create(struct zs_pool *pool, const char *name)
>> +static void zs_pool_stat_create(struct zs_pool *pool, const char *name)
>>  {
>>       struct dentry *entry;
>>
>> -     if (!zs_stat_root)
>> -             return -ENODEV;
>> +     if (!zs_stat_root) {
>> +             pr_warn("no root stat dir, not creating <%s> stat dir\n", name);
>> +             return;
>> +     }
>
> just a small nit, there are basically two warn messages now for
> `!zs_stat_root':
>
>         debugfs 'zsmalloc' stat dir creation failed
>         no root stat dir, not creating <%s> stat dir

They're logged at different times though, the first at module load
time, the second at every pool creation time.  So while they may be
logged together if the module is loaded because a pool is being
created, any later pools created will only log the second message.

>
> may be we need only one of them; but no strong opinions.

If we drop either, I'd drop the first, but I think it could be useful
also in case zsmalloc is built-in or manually loaded without creating
a pool.

>
>         -ss

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#1405076

On Thu, May 19, 2016 at 11:18:43AM -0400, Dan Streetman wrote:
> Change the return type of zs_pool_stat_create() to void, and
> remove the logic to abort pool creation if the stat debugfs
> dir/file could not be created.
> 
> The debugfs stat file is for debugging/information only, and doesn't
> affect operation of zsmalloc; there is no reason to abort creating
> the pool if the stat file can't be created.  This was seen with
> zswap, which used the same name for all pool creations, which caused
> zsmalloc to fail to create a second pool for zswap if
> CONFIG_ZSMALLOC_STAT was enabled.
> 
> Signed-off-by: Dan Streetman <ddstreet@ieee.org>
> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> Cc: Dan Streetman <dan.streetman@canonical.com>
> Cc: Minchan Kim <minchan@kernel.org>
Acked-by: Minchan Kim <minchan@kernel.org>

However, Andrew already sent old version to upstream.

Andrew, Could you send revert patch of [1] in linus's tree and send
this instead of it if you have chance?

[1] d34f615720d1 mm/zsmalloc: don't fail if can't create debugfs info

Thanks.

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