Re: [PATCH 1/4] mtd: brcmnand: improve memory management

From: Julia Lawall
Date: Thu Nov 19 2015 - 01:13:54 EST



On Wed, 18 Nov 2015, Brian Norris wrote:

> On Wed, Nov 18, 2015 at 11:04:11PM +0100, Julia Lawall wrote:
> > This patch addresses several related memory management issues in the probe
> > function:
> >
> > 1. for_each_available_child_of_node performs an of_node_get on each
> > iteration, so a break out of the loop requires an of_node_put.
> >
> > A simplified version of the semantic patch that fixes this problem is as
> > follows (http://coccinelle.lip6.fr):
> >
> > // <smpl>
> > @@
> > expression root,e;
> > local idexpression child;
> > @@
> >
> > for_each_available_child_of_node(root, child) {
> > ... when != of_node_put(child)
> > when != e = child
> > (
> > return child;
> > |
> > + of_node_put(child);
> > ? return ...;
> > )
> > ...
> > }
> > // </smpl>
>
> Good catch again
>
> > 2. The devm_kzalloc'd data is not used if brcmnand_init_cs fails. Free it
> > immediately, using devm_kfree in this case, instead of waiting for the
> > remove function.
>
> Same
>
> > 3. If the continue is not taken, then host is added to a list, that has a
> > lifetime beyond the end of the for_each_available_child_of_node loop body.
> > Thus, of_node_get is needed on child, which is referenced by host. A
> > corresponding of_node_put is needed in the remove function.
>
> This one's a bit silly. We really shouldn't be keeping the reference in
> 'host' at all. Also, as of commit 215a02fd3087 ("mtd: grab a reference to
> the MTD of_node before registering it"), the MTD core will actually be
> refcounting the node for us, too, so this isn't really necessary.
>
> I have a patch to remove brcmnand_host::of_node (appended below), which
> should make this step obsolete, and be more obvious that no extra
> of_node_get()'ing is required.

OK. Should I resend my patch without this change?

julia

> > Signed-off-by: Julia Lawall <Julia.Lawall@xxxxxxx>
> >
> > ---
> >
> > One could consider whether the of_node_get should be on host->of_node,
> > which looks more similar to the thing that is stored in the list. I used
> > child, to be more similar to the of_node_put in the same function.
> >
> > drivers/mtd/nand/brcmnand/brcmnand.c | 14 ++++++++++----
> > 1 file changed, 10 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/mtd/nand/brcmnand/brcmnand.c b/drivers/mtd/nand/brcmnand/brcmnand.c
> > index 2a437c7..b0cb55d 100644
> > --- a/drivers/mtd/nand/brcmnand/brcmnand.c
> > +++ b/drivers/mtd/nand/brcmnand/brcmnand.c
> > @@ -2237,16 +2237,20 @@ int brcmnand_probe(struct platform_device *pdev, struct brcmnand_soc *soc)
> > struct brcmnand_host *host;
> >
> > host = devm_kzalloc(dev, sizeof(*host), GFP_KERNEL);
> > - if (!host)
> > + if (!host) {
> > + of_node_put(child);
> > return -ENOMEM;
>
> In code reading, I noticed that we don't actually cleanup for prior
> iterations of brcmnand_init_cs() here. i.e., if we're exiting here, we
> should be doing nand_release() on all previously-registered chips.
>
> > + }
> > host->pdev = pdev;
> > host->ctrl = ctrl;
> > host->of_node = child;
> >
> > ret = brcmnand_init_cs(host);
> > - if (ret)
> > + if (ret) {
> > + devm_kfree(dev, host);
> > continue; /* Try all chip-selects */
> > -
> > + }
> > + of_node_get(child);
> > list_add_tail(&host->node, &ctrl->host_list);
> > }
> > }
> > @@ -2264,8 +2268,10 @@ int brcmnand_remove(struct platform_device *pdev)
> > struct brcmnand_controller *ctrl = dev_get_drvdata(&pdev->dev);
> > struct brcmnand_host *host;
> >
> > - list_for_each_entry(host, &ctrl->host_list, node)
> > + list_for_each_entry(host, &ctrl->host_list, node) {
> > + of_node_put(host->of_node);
> > nand_release(&host->mtd);
> > + }
> >
> > dev_set_drvdata(&pdev->dev, NULL);
> >
>
> Patch to kill off some of this:
>
> ---8<---
> From 6c51a9ef1325e7b06a7623c1fbca1adf6eeb8253 Mon Sep 17 00:00:00 2001
> From: Brian Norris <computersforpeace@xxxxxxxxx>
> Date: Wed, 18 Nov 2015 14:33:24 -0800
> Subject: [PATCH] mtd: brcmnand: drop brcmnand_host::of_node field
>
> We don't actually need to stash a copy of this device_node indefinitely;
> we only need it in brcmnand_init_cs().
>
> Signed-off-by: Brian Norris <computersforpeace@xxxxxxxxx>
> Cc: <bcm-kernel-feedback-list@xxxxxxxxxxxx>
> Cc: Kamal Dasu <kdasu.kdev@xxxxxxxxx>
> ---
> drivers/mtd/nand/brcmnand/brcmnand.c | 7 ++-----
> 1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mtd/nand/brcmnand/brcmnand.c b/drivers/mtd/nand/brcmnand/brcmnand.c
> index c395b4a75fb1..351438a62aaa 100644
> --- a/drivers/mtd/nand/brcmnand/brcmnand.c
> +++ b/drivers/mtd/nand/brcmnand/brcmnand.c
> @@ -176,7 +176,6 @@ struct brcmnand_cfg {
>
> struct brcmnand_host {
> struct list_head node;
> - struct device_node *of_node;
>
> struct nand_chip chip;
> struct mtd_info mtd;
> @@ -1896,10 +1895,9 @@ static int brcmnand_setup_dev(struct brcmnand_host *host)
> return 0;
> }
>
> -static int brcmnand_init_cs(struct brcmnand_host *host)
> +static int brcmnand_init_cs(struct brcmnand_host *host, struct device_node *dn)
> {
> struct brcmnand_controller *ctrl = host->ctrl;
> - struct device_node *dn = host->of_node;
> struct platform_device *pdev = host->pdev;
> struct mtd_info *mtd;
> struct nand_chip *chip;
> @@ -2231,9 +2229,8 @@ int brcmnand_probe(struct platform_device *pdev, struct brcmnand_soc *soc)
> return -ENOMEM;
> host->pdev = pdev;
> host->ctrl = ctrl;
> - host->of_node = child;
>
> - ret = brcmnand_init_cs(host);
> + ret = brcmnand_init_cs(host, child);
> if (ret)
> continue; /* Try all chip-selects */
>
> --
> 2.6.0.rc2.230.g3dd15c0
>
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