linux-kernel - Re: [PATCH 2/3] of: Make of_find_node_by

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Date:	Tue, 20 May 2014 19:55:45 -0700
From:	Frank Rowand <frowand.list@...il.com>
To:	Grant Likely <grant.likely@...aro.org>
CC:	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	David Daney <david.daney@...ium.com>,
	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
Subject: Re: [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@...ium.com>

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

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

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

> Signed-off-by: Grant Likely <grant.likely@...aro.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@...ymobile.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@...ymobile.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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