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SubjectRe: [PATCH 2/3] of: Make of_find_node_by_path() handle /aliases
On 5/13/2014 7:58 AM, Grant Likely wrote:

> Make of_find_node_by_path() handle aliases as prefixes. To make this

> work the name search is refactored to search by path component instead

> of by full string. This should be a more efficient search, and it makes

> it possible to start a search at a subnode of a tree.

>

> Signed-off-by: David Daney <david.daney@cavium.com>

> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>

> [grant.likely: Rework to not require allocating at runtime]

> Acked-by: Rob Herring <robh@kernel.org>

> Signed-off-by: Grant Likely <grant.likely@linaro.org>

> ---

> drivers/of/base.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++----

> 1 file changed, 56 insertions(+), 4 deletions(-)



Was this patch created against a tree that has modifications to device tree

locking?
I get a hang due to deadlock when I apply it. Patch to verify the
cause is below.




From: Frank Rowand <frank.rowand@sonymobile.com>

Do not apply this patch -- it is not a valid fix. The point of this patch
is to confirm the cause of a bug.

Problem seen on 3.15-rc1 with dragonboard platform patches added.

The dragonboard hangs on boot the very first time that of_find_node_by_path()
is called:

of_find_node_by_path()
raw_spin_lock_irqsave(&devtree_lock, flags)
np = __of_find_node_by_path(np, path)
for_each_child_of_node(parent, child) {

// This is a define:
#define for_each_child_of_node(parent, child) \
for (child = of_get_next_child(parent, NULL); child != NULL; \

// Resulting in a deadlock when of_get_next_child()
// attempts to lock the same lock:
raw_spin_lock_irqsave(&devtree_lock, flags)

When this patch is applied, the first lock is commented out so the
deadlock does not occur and the boot completes.

Not-signed-off-by: Frank Rowand <frank.rowand@sonymobile.com>
---
drivers/of/base.c | 4 ++++
1 file changed, 4 insertions(+)

Index: b/drivers/of/base.c
===================================================================
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -835,13 +835,17 @@ struct device_node *of_find_node_by_path
}

/* Step down the tree matching path components */
+#if 0
raw_spin_lock_irqsave(&devtree_lock, flags);
+#endif
while (np && *path == '/') {
path++; /* Increment past '/' delimiter */
np = __of_find_node_by_path(np, path);
path = strchrnul(path, '/');
}
+#if 0
raw_spin_unlock_irqrestore(&devtree_lock, flags);
+#endif
return np;
}
EXPORT_SYMBOL(of_find_node_by_path);

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