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Message-Id: <20250919160653.507109-3-sean.anderson@linux.dev>
Date: Fri, 19 Sep 2025 12:06:53 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Suzuki K Poulose <suzuki.poulose@....com>,
coresight@...ts.linaro.org,
linux-arm-kernel@...ts.infradead.org
Cc: James Clark <james.clark@...aro.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Yeoreum Yun <yeoreum.yun@....com>,
Leo Yan <leo.yan@....com>,
Linu Cherian <lcherian@...vell.com>,
Mike Leach <mike.leach@...aro.org>,
linux-kernel@...r.kernel.org,
Sean Anderson <sean.anderson@...ux.dev>
Subject: [PATCH v4 2/2] coresight: Fix possible deadlock in coresight_panic_cb
Panics can occur at any time, so taking locks may cause a deadlock (such
as if the panicking CPU held the lock). coresight_panic_cb uses
bus_for_each_dev, but that calls bus_to_subsys which takes
bus_kset->list_lock.
Instead of registering a single panic notifier and iterating over
coresight devices, register a panic notifier for each coresight device
that requires it (letting the atomic notifier list handle iteration).
atomic_notifier_chain_unregister will just return -ENOENT if a notifier
block isn't on the list, so it's safe to call when we haven't registered
a notifier.
Fixes: 46006ceb5d02 ("coresight: core: Add provision for panic callbacks")
Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
---
Changes in v4:
- Move the panic notifier into csdev and restore the panic sync API
Changes in v3:
- Rewrite patch to remove the panic sync API entirely
Changes in v2:
- Add a comment describing csdev_lock/list
- Consolidate list removal in coresight_device_release
drivers/hwtracing/coresight/coresight-core.c | 67 ++++++++------------
include/linux/coresight.h | 2 +
2 files changed, 27 insertions(+), 42 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index 022c8384b98d..6dfb1198c16e 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -1046,8 +1046,11 @@ static void coresight_device_release(struct device *dev)
{
struct coresight_device *csdev = to_coresight_device(dev);
- fwnode_handle_put(csdev->dev.fwnode);
+ if (panic_ops(csdev))
+ atomic_notifier_chain_unregister(&panic_notifier_list,
+ &csdev->panic_notifier);
free_percpu(csdev->perf_sink_id_map.cpu_map);
+ fwnode_handle_put(csdev->dev.fwnode);
kfree(csdev);
}
@@ -1315,6 +1318,16 @@ void coresight_release_platform_data(struct coresight_device *csdev,
coresight_remove_conns_sysfs_group(csdev);
}
+static int coresight_panic_notifier(struct notifier_block *nb,
+ unsigned long action, void *data)
+{
+ struct coresight_device *csdev =
+ container_of(nb, struct coresight_device, panic_notifier);
+
+ panic_ops(csdev)->sync(csdev);
+ return NOTIFY_DONE;
+}
+
struct coresight_device *coresight_register(struct coresight_desc *desc)
{
int ret;
@@ -1357,6 +1370,17 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
goto err_out;
}
}
+
+ if (panic_ops(csdev)) {
+ csdev->panic_notifier.notifier_call = coresight_panic_notifier;
+ ret = atomic_notifier_chain_register(&panic_notifier_list,
+ &csdev->panic_notifier);
+ if (ret) {
+ coresight_device_release(&csdev->dev);
+ goto err_out;
+ }
+ }
+
/*
* Make sure the device registration and the connection fixup
* are synchronised, so that we don't see uninitialised devices
@@ -1563,36 +1587,6 @@ 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;
@@ -1605,20 +1599,11 @@ 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);
@@ -1628,8 +1613,6 @@ 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/include/linux/coresight.h b/include/linux/coresight.h
index 4ac65c68bbf4..a7aaf9d3d01d 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -280,6 +280,7 @@ struct coresight_trace_id_map {
* @config_csdev_list: List of system configurations added to the device.
* @cscfg_csdev_lock: Protect the lists of configurations and features.
* @active_cscfg_ctxt: Context information for current active system configuration.
+ * @panic_notifier: Notifier block used to clean up during a panic
*/
struct coresight_device {
struct coresight_platform_data *pdata;
@@ -304,6 +305,7 @@ struct coresight_device {
struct list_head config_csdev_list;
raw_spinlock_t cscfg_csdev_lock;
void *active_cscfg_ctxt;
+ struct notifier_block panic_notifier;
};
/*
--
2.35.1.1320.gc452695387.dirty
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