[PATCH] coresight: Fix possible deadlock in coresight_panic_cb()

[Sean Anderson]

coresight_panic_cb() is called during a panic. It invokes
bus_for_each_dev(), which then calls bus_to_subsys() and takes the
'bus_kset->list_lock'. If a panic occurs after the lock has been
acquired, it can lead to a deadlock.

Instead of using a common panic notifier to iterate the bus, this commit
directly registers the TMC device's panic notifier. This avoids bus
iteration and effectively eliminates the race condition that could cause
the deadlock.

Fixes: 46006ceb5d02 ("coresight: core: Add provision for panic callbacks")
Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxxx>
Signed-off-by: Leo Yan <leo.yan@xxxxxxx>
---
 drivers/hwtracing/coresight/coresight-core.c  | 42 -------------------
 .../hwtracing/coresight/coresight-tmc-core.c  | 26 ++++++++++++
 drivers/hwtracing/coresight/coresight-tmc.h   |  2 +
 3 files changed, 28 insertions(+), 42 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index 3267192f0c1c..cb0cc8d77056 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -21,7 +21,6 @@
 #include <linux/property.h>
 #include <linux/delay.h>
 #include <linux/pm_runtime.h>
-#include <linux/panic_notifier.h>
 
 #include "coresight-etm-perf.h"
 #include "coresight-priv.h"
@@ -1566,36 +1565,6 @@ const struct bus_type coresight_bustype = {
 	.name	= "coresight",
 };
 
-static int coresight_panic_sync(struct device *dev, void *data)
-{
-	int mode;
-	struct coresight_device *csdev;
-
-	/* Run through panic sync handlers for all enabled devices */
-	csdev = container_of(dev, struct coresight_device, dev);
-	mode = coresight_get_mode(csdev);
-
-	if ((mode == CS_MODE_SYSFS) || (mode == CS_MODE_PERF)) {
-		if (panic_ops(csdev))
-			panic_ops(csdev)->sync(csdev);
-	}
-
-	return 0;
-}
-
-static int coresight_panic_cb(struct notifier_block *self,
-			       unsigned long v, void *p)
-{
-	bus_for_each_dev(&coresight_bustype, NULL, NULL,
-				 coresight_panic_sync);
-
-	return 0;
-}
-
-static struct notifier_block coresight_notifier = {
-	.notifier_call = coresight_panic_cb,
-};
-
 static int __init coresight_init(void)
 {
 	int ret;
@@ -1608,20 +1577,11 @@ static int __init coresight_init(void)
 	if (ret)
 		goto exit_bus_unregister;
 
-	/* Register function to be called for panic */
-	ret = atomic_notifier_chain_register(&panic_notifier_list,
-					     &coresight_notifier);
-	if (ret)
-		goto exit_perf;
-
 	/* initialise the coresight syscfg API */
 	ret = cscfg_init();
 	if (!ret)
 		return 0;
 
-	atomic_notifier_chain_unregister(&panic_notifier_list,
-					     &coresight_notifier);
-exit_perf:
 	etm_perf_exit();
 exit_bus_unregister:
 	bus_unregister(&coresight_bustype);
@@ -1631,8 +1591,6 @@ static int __init coresight_init(void)
 static void __exit coresight_exit(void)
 {
 	cscfg_exit();
-	atomic_notifier_chain_unregister(&panic_notifier_list,
-					     &coresight_notifier);
 	etm_perf_exit();
 	bus_unregister(&coresight_bustype);
 }
diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c
index 36599c431be6..108ed9daf56d 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-core.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-core.c
@@ -21,6 +21,7 @@
 #include <linux/slab.h>
 #include <linux/dma-mapping.h>
 #include <linux/spinlock.h>
+#include <linux/panic_notifier.h>
 #include <linux/pm_runtime.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
@@ -769,6 +770,21 @@ static void register_crash_dev_interface(struct tmc_drvdata *drvdata,
 			"Valid crash tracedata found\n");
 }
 
+static int tmc_panic_cb(struct notifier_block *nb, unsigned long v, void *p)
+{
+	struct tmc_drvdata *drvdata = container_of(nb, struct tmc_drvdata,
+						   panic_notifier);
+	struct coresight_device *csdev = drvdata->csdev;
+
+	if (coresight_get_mode(csdev) == CS_MODE_DISABLED)
+		return 0;
+
+	if (panic_ops(csdev))
+		panic_ops(csdev)->sync(csdev);
+
+	return 0;
+}
+
 static int __tmc_probe(struct device *dev, struct resource *res)
 {
 	int ret = 0;
@@ -885,6 +901,12 @@ static int __tmc_probe(struct device *dev, struct resource *res)
 		goto out;
 	}
 
+	if (panic_ops(drvdata->csdev)) {
+		drvdata->panic_notifier.notifier_call = tmc_panic_cb;
+		atomic_notifier_chain_register(&panic_notifier_list,
+					       &drvdata->panic_notifier);
+	}
+
 out:
 	if (is_tmc_crashdata_valid(drvdata) &&
 	    !tmc_prepare_crashdata(drvdata))
@@ -929,6 +951,10 @@ static void __tmc_remove(struct device *dev)
 {
 	struct tmc_drvdata *drvdata = dev_get_drvdata(dev);
 
+	if (panic_ops(drvdata->csdev))
+		atomic_notifier_chain_unregister(&panic_notifier_list,
+						 &drvdata->panic_notifier);
+
 	/*
 	 * Since misc_open() holds a refcount on the f_ops, which is
 	 * etb fops in this case, device is there until last file
diff --git a/drivers/hwtracing/coresight/coresight-tmc.h b/drivers/hwtracing/coresight/coresight-tmc.h
index cbb4ba439158..873c5427673c 100644
--- a/drivers/hwtracing/coresight/coresight-tmc.h
+++ b/drivers/hwtracing/coresight/coresight-tmc.h
@@ -243,6 +243,7 @@ struct tmc_resrv_buf {
  *		(after crash) by default.
  * @crash_mdata: Reserved memory for storing tmc crash metadata.
  *		 Used by ETR/ETF.
+ * @panic_notifier: Notifier used to clean up during a panic
  */
 struct tmc_drvdata {
 	struct clk		*atclk;
@@ -273,6 +274,7 @@ struct tmc_drvdata {
 	struct etr_buf		*perf_buf;
 	struct tmc_resrv_buf	resrv_buf;
 	struct tmc_resrv_buf	crash_mdata;
+	struct notifier_block	panic_notifier;
 };
 
 struct etr_buf_operations {
-- 
2.34.1