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From: Minchan Kim <minchan@kernel.org>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Dan Streetman <ddstreet@ieee.org>,
	Seth Jennings <sjennings@variantweb.net>,
	Nitin Gupta <ngupta@vflare.org>, Juneho Choi <juno.choi@lge.com>,
	Gunho Lee <gunho.lee@lge.com>,
	Luigi Semenzato <semenzato@google.com>,
	Jerome Marchand <jmarchan@redhat.com>
Subject: Re: [PATCH v1 01/10] zram: avoid calling of zram_meta_free under init_lock
Date: Fri, 23 Jan 2015 10:03:36 +0900	[thread overview]
Message-ID: <20150123010336.GA18918@blaptop> (raw)
In-Reply-To: <20150121142115.GA986@swordfish>

Hello,

On Wed, Jan 21, 2015 at 11:21:53PM +0900, Sergey Senozhatsky wrote:
> On (01/21/15 15:14), Minchan Kim wrote:
> > We don't need to call zram_meta_free under init_lock.
> > What we need to prevent race is setting NULL into zram->meta
> > (ie, init_done). This patch does it.
> > 
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> >  drivers/block/zram/zram_drv.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index 9250b3f..7e03d86 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -719,6 +719,8 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
> >  	}
> >  
> >  	meta = zram->meta;
> > +	zram->meta = NULL;
> > +
> >  	/* Free all pages that are still in this zram device */
> >  	for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
> >  		unsigned long handle = meta->table[index].handle;
> > @@ -731,8 +733,6 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
> >  	zcomp_destroy(zram->comp);
> >  	zram->max_comp_streams = 1;
> >  
> > -	zram_meta_free(zram->meta);
> > -	zram->meta = NULL;
> >  	/* Reset stats */
> >  	memset(&zram->stats, 0, sizeof(zram->stats));
> >  
> > @@ -741,6 +741,7 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
> >  		set_capacity(zram->disk, 0);
> >  
> >  	up_write(&zram->init_lock);
> > +	zram_meta_free(meta);
> 
> Hello,
> 
> since we detached ->meta from zram, this one doesn't really need
> ->init_lock protection:
> 
> 	/* Free all pages that are still in this zram device */
> 	for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
> 		unsigned long handle = meta->table[index].handle;
> 		if (!handle)
> 			continue;
> 
> 		zs_free(meta->mem_pool, handle);
> 	}
> 
> 
> 	-ss

Good catch.

As well, we could move zcomp_destroy and memset(&zram->stats)
out of the lock but zram_rw_page, ZRAM_ATTR_RO, disksize_show
and orig_data_size_show have a race bug which access stats
out of the lock so that it could show the stale vaule.
Although it's not a significant, there is no reason to hesitate the fix. :)

I will fix it. Thanks!


> 
> >  	/*
> >  	 * Revalidate disk out of the init_lock to avoid lockdep splat.
> > -- 
> > 1.9.3
> > 

  reply	other threads:[~2015-01-23  1:03 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-21  6:14 [PATCH v1 00/10] zsmalloc compaction support Minchan Kim
2015-01-21  6:14 ` [PATCH v1 01/10] zram: avoid calling of zram_meta_free under init_lock Minchan Kim
2015-01-21 14:21   ` Sergey Senozhatsky
2015-01-23  1:03     ` Minchan Kim [this message]
2015-01-23  1:15       ` Minchan Kim
2015-01-21  6:14 ` [PATCH v1 02/10] zsmalloc: decouple handle and object Minchan Kim
2015-01-26  2:53   ` Ganesh Mahendran
2015-01-27  3:27     ` Minchan Kim
2015-01-21  6:14 ` [PATCH v1 03/10] zsmalloc: implement reverse mapping Minchan Kim
2015-01-21  6:14 ` [PATCH v1 04/10] zsmalloc: factor out obj_[malloc|free] Minchan Kim
2015-01-21  6:14 ` [PATCH v1 05/10] zsmalloc: add status bit Minchan Kim
2015-01-21  6:14 ` [PATCH v1 06/10] zsmalloc: support compaction Minchan Kim
2015-01-21  6:14 ` [PATCH v1 07/10] zsmalloc: adjust ZS_ALMOST_FULL Minchan Kim
2015-01-21  6:14 ` [PATCH v1 08/10] zram: support compaction Minchan Kim
2015-01-21  6:14 ` [PATCH v1 09/10] zsmalloc: add fullness into stat Minchan Kim
2015-01-21  6:14 ` [PATCH v1 10/10] zsmalloc: record handle in page->private for huge object Minchan Kim

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