Re: [PATCH] zram: move comp allocation out of init_lock

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

On (03/05/14 15:57), Jerome Marchand wrote:
> On 03/04/2014 11:10 AM, Sergey Senozhatsky wrote:
> > While fixing lockdep spew of ->init_lock reported by Sasha Levin [1], Minchan
> > Kim noted [2] that it's better to move compression backend allocation (using
> > GPF_KERNEL) out of the ->init_lock lock, same way as with zram_meta_alloc(),
> > in order to prevent the same lockdep spew.
> > 
> > [1] https://lkml.org/lkml/2014/2/27/337
> > [2] https://lkml.org/lkml/2014/3/3/32
> > 
> > Cc: Sasha Levin <sasha.levin@oracle.com>
> > Reported-by: Minchan Kim <minchan@kernel.org>
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> > ---
> >  drivers/block/zram/zram_drv.c | 27 +++++++++++++++------------
> >  1 file changed, 15 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index 15d46f2..e4d536b 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -580,9 +580,10 @@ 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;
> > +	int err = -EINVAL;
> >  
> >  	disksize = memparse(buf, NULL);
> >  	if (!disksize)
> > @@ -593,30 +594,32 @@ static ssize_t disksize_store(struct device *dev,
> >  	if (!meta)
> >  		return -ENOMEM;
> >  
> > +	comp = zcomp_create(zram->compressor, zram->max_comp_streams);
> > +	if (!comp) {
> > +		pr_info("Cannot initialise %s compressing backend\n",
> > +				zram->compressor);
> > +		goto out_cleanup;
> > +	}
> > +
> 
> zcomp_create() could fail because of a failed allocation, in which case
> ENOMEM would be more appropriate. I guess zcomp_create() should return
> an errno in case of failure.
> But that's an other problem than the one addressed in this patch:
> 

There are two possible cases of failed zcomp_create(). One is,
you're right, -ENOMEM. The second one is request of unsupported
compression algorithm - -EINVAL. agree, it makes sense to return
ERR_PTR() from zcomp_create(): -EINVAL or -ENOMEM.

	-ss

> Acked-by: Jerome Marchand <jmarchan@redhat.com>
> 
> >  	down_write(&zram->init_lock);
> >  	if (init_done(zram)) {
> > +		up_write(&zram->init_lock);
> >  		pr_info("Cannot change disksize for initialized device\n");
> >  		err = -EBUSY;
> > -		goto out_free_meta;
> > -	}
> > -
> > -	zram->comp = zcomp_create(zram->compressor, zram->max_comp_streams);
> > -	if (!zram->comp) {
> > -		pr_info("Cannot initialise %s compressing backend\n",
> > -				zram->compressor);
> > -		err = -EINVAL;
> > -		goto out_free_meta;
> > +		goto out_cleanup;
> >  	}
> >  
> >  	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_free_meta:
> > -	up_write(&zram->init_lock);
> > +out_cleanup:
> > +	if (comp)
> > +		zcomp_destroy(comp);
> >  	zram_meta_free(meta);
> >  	return err;
> >  }
> > 
>