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Date: Thu, 22 Jan 2015 16:14:46 +0000
From: Grant Likely <grant.likely@...aro.org>
To: Geert Uytterhoeven <geert+renesas@...der.be>,
Rob Herring <robh+dt@...nel.org>
Cc: Gaurav Minocha <gaurav.minocha.os@...il.com>,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH] of: Add missing of_node_put() in of_find_node_by_path()
On Wed, 14 Jan 2015 16:45:56 +0100
, Geert Uytterhoeven <geert+renesas@...der.be>
wrote:
> When traversing all nodes and moving to a new path component, the old
> one must be released by calling of_node_put(). Else the refcounts of the
> parent node(s) will not be decremented.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> Background.
>
> While investigating a reference count imbalance issue with
> CONFIG_OF_DYNAMIC=y, I wrote the debug code below to validate the
> reference counts of the nodes I was interested in.
> During the first call of check_refcnts(), it gathers all reference
> counts. During a subsequent call, it verifies that they are still the
> same.
>
> Surprisingly, lots of reference counts were wrong, and kept incrementing
> every time check_refcnts() was called.
Yup, reference counting is a mess. We definitely need tests to make sure
the core code does the right things with them.
> I was just wondering whether it would be useful to have a reference
> count test in OF_UNITTEST, but now I see the "select OF_DYNAMIC" will go
> away?
select OF_DYNAMIC is going away, but that only so that unittests work
with both OF_DYNAMIC and !OF_DYANMIC. Instead there will be some
unittests that are only run when OF_DYNAMIC is selected.
>
> Feel free to (ab)use the code below and derive a unittest from it...
>
> static struct to_check {
> const char *path;
> int refcnt;
> } to_check[] = {
> { "/" },
> { "/cpus/cpu@0" },
> { "/cpus/cpu@1" },
> /* ... other paths I was interested in ... */
> };
>
> static void check_refcnts(void)
> {
> static bool called;
> unsigned int i;
> const char *path;
> struct device_node *np;
> int refcnt;
> unsigned int errors = 0;
>
> pr_info("----- %s reference counts -----\n",
> called ? "Checking" : "Saving");
> for (i = 0; i < ARRAY_SIZE(to_check); i++) {
> path = to_check[i].path;
> np = of_find_node_by_path(path);
> if (!np)
> continue;
>
> refcnt = atomic_read(&np->kobj.kref.refcount);
> if (!called) {
> pr_info("%s %d\n", path, refcnt);
> to_check[i].refcnt = refcnt;
> } else if (refcnt == to_check[i].refcnt) {
> pr_info("%s %d (OK)\n", path, refcnt);
> } else {
> pr_info("%s %d (should be %d)\n", path, refcnt,
> to_check[i].refcnt);
> errors++;
> }
>
> of_node_put(np);
> }
>
> if (called)
> pr_info("----- Checking done (%u errors) -----\n", errors);
> else
> pr_info("----- Saving done -----\n");
>
> called = true;
> }
> ---
> drivers/of/base.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 36536b6a8834acd2..f3e346e19c69d1f2 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -791,8 +791,10 @@ struct device_node *of_find_node_opts_by_path(const char *path, const char **opt
> if (!np)
> np = of_node_get(of_root);
> while (np && *path == '/') {
> + struct device_node *parent = np;
> path++; /* Increment past '/' delimiter */
> - np = __of_find_node_by_path(np, path);
> + np = __of_find_node_by_path(parent, path);
> + of_node_put(parent);
> path = strchrnul(path, '/');
> }
> raw_spin_unlock_irqrestore(&devtree_lock, flags);
This doesn't look /quite/ the best. __for_each_child_of_node() is
fiddling with refcounts, but the '__' of functions shouldn't need to do
that since they are called under the spinlock (nothing is going to
change while they are called). __of_find_all_nodes() for instance
doesn't do refcounting, but of_find_all_nodes() does.
Does the following also solve the problem?
g.
---
diff --git a/drivers/of/base.c b/drivers/of/base.c
index 36536b6a8834..0357b51a7440 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -626,9 +626,8 @@ static struct device_node *__of_get_next_child(const struct device_node *node,
next = prev ? prev->sibling : node->child;
for (; next; next = next->sibling)
- if (of_node_get(next))
+ if (next)
break;
- of_node_put(prev);
return next;
}
#define __for_each_child_of_node(parent, child) \
@@ -650,7 +649,8 @@ struct device_node *of_get_next_child(const struct device_node *node,
unsigned long flags;
raw_spin_lock_irqsave(&devtree_lock, flags);
- next = __of_get_next_child(node, prev);
+ next = of_node_get(__of_get_next_child(node, prev));
+ of_node_put(prev);
raw_spin_unlock_irqrestore(&devtree_lock, flags);
return next;
}
@@ -789,12 +789,13 @@ struct device_node *of_find_node_opts_by_path(const char *path, const char **opt
/* Step down the tree matching path components */
raw_spin_lock_irqsave(&devtree_lock, flags);
if (!np)
- np = of_node_get(of_root);
+ np = of_root;
while (np && *path == '/') {
path++; /* Increment past '/' delimiter */
np = __of_find_node_by_path(np, path);
path = strchrnul(path, '/');
}
+ of_node_get(np);
raw_spin_unlock_irqrestore(&devtree_lock, flags);
return np;
}
--
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