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From: Vlastimil Babka <vbabka@suse.cz>
To: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: linux-mm <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-s390 <linux-s390@vger.kernel.org>,
	Faiyaz Mohammed <faiyazm@codeaurora.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm/slub: fix endianness bug for alloc/free_traces attributes
Date: Mon, 29 Nov 2021 15:26:13 +0100	[thread overview]
Message-ID: <9cd2e67b-4769-ad91-2b2a-1899bdf3f8fc@suse.cz> (raw)
In-Reply-To: <20211126171848.17534-1-gerald.schaefer@linux.ibm.com>

On 11/26/21 18:18, Gerald Schaefer wrote:
> On big-endian s390, the alloc/free_traces attributes produce endless
> output, because of always 0 idx in slab_debugfs_show().
> 
> idx is de-referenced from *v, which points to a loff_t value, with
> 
> unsigned int idx = *(unsigned int *)v;
> 
> This will only give the upper 32 bits on big-endian, which remain 0.
> 
> Instead of only fixing this de-reference, during discussion it seemed
> more appropriate to change the seq_ops so that they use an explicit
> iterator in private loc_track struct.
> 
> This patch adds idx to loc_track, which will also fix the endianness bug.
> 
> Link: https://lore.kernel.org/r/20211117193932.4049412-1-gerald.schaefer@linux.ibm.com
> Fixes: 64dd68497be7 ("mm: slub: move sysfs slab alloc/free interfaces to debugfs")
> Cc: <stable@vger.kernel.org> # v5.14+
> Reported-by: Steffen Maier <maier@linux.ibm.com>
> Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

With a nit below:

> ---
>  mm/slub.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index a8626825a829..abe7db581d68 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5081,6 +5081,7 @@ struct loc_track {
>  	unsigned long max;
>  	unsigned long count;
>  	struct location *loc;
> +	loff_t idx;
>  };
>  
>  static struct dentry *slab_debugfs_root;
> @@ -6052,11 +6053,11 @@ __initcall(slab_sysfs_init);
>  #if defined(CONFIG_SLUB_DEBUG) && defined(CONFIG_DEBUG_FS)
>  static int slab_debugfs_show(struct seq_file *seq, void *v)
>  {
> -
> -	struct location *l;
> -	unsigned int idx = *(unsigned int *)v;
>  	struct loc_track *t = seq->private;
> +	struct location *l;
> +	unsigned long idx;
>  
> +	idx = (unsigned long) t->idx;
>  	if (idx < t->count) {
>  		l = &t->loc[idx];
>  
> @@ -6105,16 +6106,18 @@ static void *slab_debugfs_next(struct seq_file *seq, void *v, loff_t *ppos)
>  {
>  	struct loc_track *t = seq->private;
>  
> -	v = ppos;
> -	++*ppos;
> +	t->idx = ++(*ppos);
>  	if (*ppos <= t->count)
> -		return v;
> +		return ppos;

What I had in mind, and to be more in line with the seq_file example, would
be to return &t->idx here. Then it's what gets passed to slab_debugfs_show()
as 'v'. But since we ignore 'v' there, it probably doesn't matter.

>  
>  	return NULL;
>  }
>  
>  static void *slab_debugfs_start(struct seq_file *seq, loff_t *ppos)
>  {
> +	struct loc_track *t = seq->private;
> +
> +	t->idx = *ppos;
>  	return ppos;

And same here.

>  }
>  
> 


  reply	other threads:[~2021-11-29 14:28 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-17 19:39 [RFC PATCH 0/1] mm/slub: endless "No data" printing for alloc/free_traces attribute Gerald Schaefer
2021-11-17 19:39 ` [RFC PATCH 1/1] mm/slub: fix " Gerald Schaefer
2021-11-19 10:41   ` Vlastimil Babka
2021-11-19 19:59     ` Gerald Schaefer
2021-11-22 15:02       ` Vlastimil Babka
2021-11-22 20:14         ` Gerald Schaefer
2021-11-22 20:33           ` Gerald Schaefer
2021-11-23 14:19             ` Vlastimil Babka
2021-11-25 16:13               ` Gerald Schaefer
2021-11-25 20:12                 ` Gerald Schaefer
2021-11-25 22:00                   ` Vlastimil Babka
2021-11-26 17:11                     ` Gerald Schaefer
2021-11-26 17:18                     ` [PATCH] mm/slub: fix endianness bug for alloc/free_traces attributes Gerald Schaefer
2021-11-29 14:26                       ` Vlastimil Babka [this message]
2021-11-19  9:43 ` [RFC PATCH 0/1] mm/slub: endless "No data" printing for alloc/free_traces attribute Vlastimil Babka

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