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Subject: [PATCH] driver core: Add a guard() definition for the device_lock()
From:   Dan Williams <dan.j.williams@intel.com>
To:     gregkh@linuxfoundation.org
Cc:     Vishal Verma <vishal.l.verma@intel.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org,
        nvdimm@lists.linux.dev
Date:   Wed, 13 Dec 2023 15:02:35 -0800
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At present there are ~200 usages of device_lock() in the kernel. Some of
those usages lead to "goto unlock;" patterns which have proven to be
error prone. Define a "device" guard() definition to allow for those to
be cleaned up and prevent new ones from appearing.

Link: http://lore.kernel.org/r/657897453dda8_269bd29492@dwillia2-mobl3.amr.corp.intel.com.notmuch
Link: http://lore.kernel.org/r/6577b0c2a02df_a04c5294bb@dwillia2-xfh.jf.intel.com.notmuch
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
Hi Greg,

I wonder if you might include this change in v6.7-rc to ease some patch
sets alternately going through my tree and Andrew's tree. Those
discussions are linked above. Alternately I can can just take it through
my tree with your ack and the other use case can circle back to it in
the v6.9 cycle.

I considered also defining a __free() helper similar to __free(mutex),
but I think "__free(device)" would be a surprising name for something
that drops a lock. Also, I like the syntax of guard(device) over
something like guard(device_lock) since a 'struct device *' is the
argument, not a lock type, but I'm open to your or Peter's thoughts on
the naming.

 include/linux/device.h |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/device.h b/include/linux/device.h
index d7a72a8749ea..6c83294395ac 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1007,6 +1007,8 @@ static inline void device_unlock(struct device *dev)
 	mutex_unlock(&dev->mutex);
 }
 
+DEFINE_GUARD(device, struct device *, device_lock(_T), device_unlock(_T))
+
 static inline void device_lock_assert(struct device *dev)
 {
 	lockdep_assert_held(&dev->mutex);