Re: [PATCH v2 13/11] mtd: assign mtd->dev.of_node when creating partition devices

[Boris Brezillon]

Hi Brian,

On Wed, 11 Nov 2015 16:15:50 -0800
Brian Norris <computersforpeace@xxxxxxxxx> wrote:

> On Mon, Nov 02, 2015 at 01:38:41AM +0100, Boris Brezillon wrote:
> > MTD partitions may have been created from a DT definition, and in this case
> > the ->of_node of the struct device embedded in mtd_info should point to
> > the DT node that was used to create the partition.
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx>
> 
> I like the idea of this patch, but I'm not sure about all of its
> details.
> 
> > ---
> > Hi Brian,
> > 
> > Yet another patch that IMO should go into your "mtd: migrate 'of_node'
> > handling to core, not in mtd_part_parser_data" series.
> > 
> > Best Regards,
> > 
> > Boris
> > 
> >  drivers/mtd/mtdcore.c          | 17 +++++++++++++----
> >  drivers/mtd/mtdpart.c          |  3 +++
> >  drivers/mtd/ofpart.c           |  1 +
> >  include/linux/mtd/partitions.h |  1 +
> >  4 files changed, 18 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> > index b1eea48..6101288 100644
> > --- a/drivers/mtd/mtdcore.c
> > +++ b/drivers/mtd/mtdcore.c
> > @@ -32,6 +32,7 @@
> >  #include <linux/err.h>
> >  #include <linux/ioctl.h>
> >  #include <linux/init.h>
> > +#include <linux/of.h>
> >  #include <linux/proc_fs.h>
> >  #include <linux/idr.h>
> >  #include <linux/backing-dev.h>
> > @@ -584,11 +585,13 @@ int mtd_device_parse_register(struct mtd_info *mtd, const char * const *types,
> >  			      const struct mtd_partition *parts,
> >  			      int nr_parts)
> >  {
> > -	int ret;
> > +	int ret, i;
> >  	struct mtd_partition *real_parts = NULL;
> >  
> >  	ret = parse_mtd_partitions(mtd, types, &real_parts, parser_data);
> > -	if (ret <= 0 && nr_parts && parts) {
> > +	if (ret > 0) {
> > +		nr_parts = ret;
> > +	} else if (nr_parts && parts) {
> >  		real_parts = kmemdup(parts, sizeof(*parts) * nr_parts,
> >  				     GFP_KERNEL);
> >  		if (!real_parts)
> > @@ -604,7 +607,7 @@ int mtd_device_parse_register(struct mtd_info *mtd, const char * const *types,
> >  		ret = 0;
> >  	}
> >  
> > -	ret = mtd_add_device_partitions(mtd, real_parts, ret);
> > +	ret = mtd_add_device_partitions(mtd, real_parts, nr_parts);
> >  	if (ret)
> >  		goto out;
> >  
> > @@ -623,7 +626,13 @@ int mtd_device_parse_register(struct mtd_info *mtd, const char * const *types,
> >  	}
> >  
> >  out:
> > -	kfree(real_parts);
> > +	if (real_parts) {
> > +		for (i = 0; i < nr_parts; i++)
> > +			of_node_put(real_parts[i].of_node);
> > +
> > +		kfree(real_parts);
> > +	}
> > +
> >  	return ret;
> >  }
> >  EXPORT_SYMBOL_GPL(mtd_device_parse_register);
> > diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
> > index f8ba153..95f3a0d 100644
> > --- a/drivers/mtd/mtdpart.c
> > +++ b/drivers/mtd/mtdpart.c
> > @@ -29,6 +29,7 @@
> >  #include <linux/kmod.h>
> >  #include <linux/mtd/mtd.h>
> >  #include <linux/mtd/partitions.h>
> > +#include <linux/of.h>
> >  #include <linux/err.h>
> >  #include <linux/kconfig.h>
> >  
> > @@ -319,6 +320,7 @@ static int part_block_markbad(struct mtd_info *mtd, loff_t ofs)
> >  
> >  static inline void free_partition(struct mtd_part *p)
> >  {
> > +	of_node_put(mtd_get_of_node(&p->mtd));
> >  	kfree(p->mtd.name);
> >  	kfree(p);
> >  }
> > @@ -391,6 +393,7 @@ static struct mtd_part *allocate_partition(struct mtd_info *master,
> >  	slave->mtd.dev.parent = IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER) ?
> >  				&master->dev :
> >  				master->dev.parent;
> > +	mtd_set_of_node(&slave->mtd, of_node_get(part->of_node));
> >  
> >  	slave->mtd._read = part_read;
> >  	slave->mtd._write = part_write;
> > diff --git a/drivers/mtd/ofpart.c b/drivers/mtd/ofpart.c
> > index f78d2ae..5c64e04 100644
> > --- a/drivers/mtd/ofpart.c
> > +++ b/drivers/mtd/ofpart.c
> > @@ -111,6 +111,7 @@ static int parse_ofpart_partitions(struct mtd_info *master,
> >  		if (of_get_property(pp, "lock", &len))
> >  			(*pparts)[i].mask_flags |= MTD_POWERUP_LOCK;
> >  
> > +		(*pparts)[i].of_node = of_node_get(pp);
> 
> I don't think we should mix up too much of the error handling between
> ofpart.c and mtdcore.c (right now, you do of_node_get() here but the
> of_node_put() is forced into mtdcore.c). I think the problem here is the
> same as the problem with Linus' patch here:
> 
> http://lists.infradead.org/pipermail/linux-mtd/2015-November/063219.html
> 
> It's just too easy to leak resources when MTD parsers don't have their
> own cleanup functions (like C++ destructors, or the driver model's
> remove() function, or so many other resource models). If we had a
> cleanup function, then we could just put the release handling there.
> 
> But actually, I don't think we need to 'get' the property here; we only
> need to 'get' it when we're putting it somewhere that will actually use
> it long term. i.e., when it actually gets assigned to the
> mtd.dev.of_node field and is headed for sysfs.
> 
> IOW, I think we can grab the reference in add_mtd_device() and drop it
> in del_mtd_device(). This would handle both the partition and
> non-partition case the same.

Hm, actually I think we need it. When you iterate over child nodes with
for_each_child_of_node(), the node is released (of_node_put() is
called) after each iteration. While this is not a problem for mtd
device registration (because the controller usually retain the
reference when add_mtd_device() is called), this is not true for the
partitions. And if the partitions are ever defined using an overlay,
this can be a problem.

To sum-up, I think we should retain the node reference until
add_mtd_device() has retained it, so maybe we should have a ->cleanup()
function in mtd part parsers.

Best Regards,

Boris

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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