[PATCH] coresight: Fix possible deadlock with lock dependency

[Sudeep Holla]

With lockdeps enabled, we get the following warning:

======================================================
WARNING: possible circular locking dependency detected
------------------------------------------------------
kworker/u12:1/53 is trying to acquire lock:
ffff80000adce220 (coresight_mutex){+.+.}-{4:4}, at: coresight_set_assoc_ectdev_mutex+0x3c/0x5c
but task is already holding lock:
ffff80000add1f60 (ect_mutex){+.+.}-{4:4}, at: cti_probe+0x318/0x394

which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:

-> #1 (ect_mutex){+.+.}-{4:4}:
       __mutex_lock_common+0xd8/0xe60
       mutex_lock_nested+0x44/0x50
       cti_add_assoc_to_csdev+0x4c/0x184
       coresight_register+0x2f0/0x314
       tmc_probe+0x33c/0x414

-> #0 (coresight_mutex){+.+.}-{4:4}:
       __lock_acquire+0x1a20/0x32d0
       lock_acquire+0x160/0x308
       __mutex_lock_common+0xd8/0xe60
       mutex_lock_nested+0x44/0x50
       coresight_set_assoc_ectdev_mutex+0x3c/0x5c
       cti_update_conn_xrefs+0x6c/0xf8
       cti_probe+0x33c/0x394

other info that might help us debug this:
 Possible unsafe locking scenario:
       CPU0                    CPU1
       ----                    ----
  lock(ect_mutex);
                               lock(coresight_mutex);
                               lock(ect_mutex);
  lock(coresight_mutex);
 *** DEADLOCK ***

4 locks held by kworker/u12:1/53:
 #0: ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x1fc/0x63c
 #1: (deferred_probe_work){+.+.}-{0:0}, at: process_one_work+0x228/0x63c
 #2: (&dev->mutex){....}-{4:4}, at: __device_attach+0x48/0x1a8
 #3: (ect_mutex){+.+.}-{4:4}, at: cti_probe+0x318/0x394

To fix the same, call cti_add_assoc_to_csdev without the holding
coresight_mutex and confine the locking while setting the associated
ect / cti device using coresight_set_assoc_ectdev_mutex().

Cc: Mathieu Poirier <mathieu.poirier at linaro.org>
Cc: Suzuki K Poulose <suzuki.poulose at arm.com>
Cc: Mike Leach <mike.leach at linaro.org>
Cc: Leo Yan <leo.yan at linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla at arm.com>
---
 drivers/hwtracing/coresight/coresight-core.c     | 7 ++++---
 drivers/hwtracing/coresight/coresight-cti-core.c | 5 +++--
 2 files changed, 7 insertions(+), 5 deletions(-)

Hi,

I am not sure if I missed to consider something, but this is something
I think could be the fix.

Regards,
Sudeep

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index 1edfec1e9d18..275b4dce8401 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -1659,14 +1659,15 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 		ret = coresight_fixup_device_conns(csdev);
 	if (!ret)
 		ret = coresight_fixup_orphan_conns(csdev);
-	if (!ret && cti_assoc_ops && cti_assoc_ops->add)
-		cti_assoc_ops->add(csdev);
 
 out_unlock:
 	mutex_unlock(&coresight_mutex);
 	/* Success */
-	if (!ret)
+	if (!ret) {
+		if (cti_assoc_ops && cti_assoc_ops->add)
+			cti_assoc_ops->add(csdev);
 		return csdev;
+	}
 
 	/* Unregister the device if needed */
 	if (registered) {
diff --git a/drivers/hwtracing/coresight/coresight-cti-core.c b/drivers/hwtracing/coresight/coresight-cti-core.c
index 8988b2ed2ea6..1be92342b5b9 100644
--- a/drivers/hwtracing/coresight/coresight-cti-core.c
+++ b/drivers/hwtracing/coresight/coresight-cti-core.c
@@ -541,7 +541,7 @@ cti_match_fixup_csdev(struct cti_device *ctidev, const char *node_name,
 /*
  * Search the cti list to add an associated CTI into the supplied CS device
  * This will set the association if CTI declared before the CS device.
- * (called from coresight_register() with coresight_mutex locked).
+ * (called from coresight_register() without coresight_mutex locked).
  */
 static void cti_add_assoc_to_csdev(struct coresight_device *csdev)
 {
@@ -569,7 +569,8 @@ static void cti_add_assoc_to_csdev(struct coresight_device *csdev)
 			 * if we found a matching csdev then update the ECT
 			 * association pointer for the device with this CTI.
 			 */
-			csdev->ect_dev = ect_item->csdev;
+			coresight_set_assoc_ectdev_mutex(csdev->ect_dev,
+							 ect_item->csdev);
 			break;
 		}
 	}
-- 
2.37.1