linux-kernel - suggestion for lock debugging.

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Date:	Tue, 13 Feb 2007 17:58:40 -0800
From:	Ben Greear <greearb@...delatech.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: suggestion for lock debugging.

While playing around with lockdep (nice tool!) I thought
it might be nice to store the file-name and line where
the lock was acquired.  For the generic case, this could be done
with the __FILE__ and __LINE__ compiler macros, but for highly interesting
locks (ie, rtnl in my case), you could pass in the __FILE__ and __LINE__
where rtnl_lock() is called, something like:

+++ b/include/linux/rtnetlink.h
@@ -1042,7 +1042,8 @@ __rta_reserve(struct sk_buff *skb, int attrtype, int attrlen)
  extern void rtmsg_ifinfo(int type, struct net_device *dev, unsigned change);

  /* RTNL is used as a global lock for all changes to network configuration  */
-extern void rtnl_lock(void);
+#define rtnl_lock() __rtnl_lock(__FILE__, __LINE__);
+extern void __rtnl_lock(const char* fname, int fline);
  extern void rtnl_unlock(void);
  extern int rtnl_trylock(void);

/* pass this off to lockdep and have it store the info for
* later printing, instead of this current hack below that stores
* it in a global variable...
*/
+void __rtnl_lock(const char* fname, int fline)
  {
  	mutex_lock(&rtnl_mutex);
+	rtnl_locked_fname = fname;
+	rtnl_locked_fline = fline;
  }

I have a hacked up patch that allows lockdep to save and print
this info, but I'm not clear on exactly how to pass the fname, fline info
through mutex_lock and on to lockdep's methods....

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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