Re: [PATCH v3] coresight: Fix possible deadlock in coresight_panic_cb

Leo Yan
2025-09-15T09:58:32Z

On Fri, Sep 12, 2025 at 11:13:14AM -0400, Sean Anderson wrote:
> coresight_panic_cb is called with interrupts disabled during panics.
> However, bus_for_each_dev calls bus_to_subsys which takes
> bus_kset->list_lock without disabling IRQs. This may cause a deadlock.

I would rephrase it to make it clearer for anyone reading it later:

coresight_panic_cb() is called during panics, which can preempt a flow
that triggers exceptions (such as data or instruction aborts).
However, bus_for_each_dev() calls bus_to_subsys(), which takes
'bus_kset->list_lock'. If a panic occurs after the lock has been
acquired, it will cause a deadlock.

> Instead of adding a panic API for coresight devices, just have coresight
> drivers that need a panic callback register directly with the panic
> notifier.
>
> Fixes: 46006ceb5d02 ("coresight: core: Add provision for panic callbacks")
> Fixes: 6dbcbcfc4496 ("coresight: tmc: Enable panic sync handling")

Let us fix the bug caused by the commit 46006ceb5d02. OTOH, I think we
should not touch change introduced in the commit 6dbcbcfc4496.

Please see details below.

> Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
> ---
>
> 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 | 42 -------------------
> .../hwtracing/coresight/coresight-tmc-core.c | 20 ++++++++-
> .../hwtracing/coresight/coresight-tmc-etf.c | 12 +++---
> .../hwtracing/coresight/coresight-tmc-etr.c | 12 +++---
> drivers/hwtracing/coresight/coresight-tmc.h | 10 ++++-
> include/linux/coresight.h | 11 +----
> 6 files changed, 38 insertions(+), 69 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index fa758cc21827..297af270bf3d 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -19,7 +19,6 @@
> #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"
> @@ -1563,36 +1562,6 @@ 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 +1574,11 @@ 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 +1588,6 @@ 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);
> }

Removing panic notifier in coresight-core.c looks good to me.

> diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c
> index 88afb16bb6be..012f76dbf7d3 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-core.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-core.c
> @@ -16,6 +16,7 @@
> #include <linux/fs.h>
> #include <linux/miscdevice.h>
> #include <linux/mutex.h>
> +#include <linux/panic_notifier.h>
> #include <linux/property.h>
> #include <linux/uaccess.h>
> #include <linux/slab.h>
> @@ -834,6 +835,7 @@ static int __tmc_probe(struct device *dev, struct resource *res)
> desc.type = CORESIGHT_DEV_TYPE_SINK;
> desc.subtype.sink_subtype = CORESIGHT_DEV_SUBTYPE_SINK_SYSMEM;
> desc.ops = &tmc_etr_cs_ops;
> + drvdata->panic_notifier.notifier_call = tmc_panic_sync_etr;
> ret = tmc_etr_setup_caps(dev, devid, &desc.access);
> if (ret)
> goto out;
> @@ -847,6 +849,7 @@ static int __tmc_probe(struct device *dev, struct resource *res)
> desc.subtype.sink_subtype = CORESIGHT_DEV_SUBTYPE_SINK_BUFFER;
> desc.subtype.link_subtype = CORESIGHT_DEV_SUBTYPE_LINK_FIFO;
> desc.ops = &tmc_etf_cs_ops;
> + drvdata->panic_notifier.notifier_call = tmc_panic_sync_etf;
> dev_list = &etf_devs;
> break;
> default:
> @@ -869,11 +872,18 @@ static int __tmc_probe(struct device *dev, struct resource *res)
> dev->platform_data = pdata;
> desc.pdata = pdata;
>
> + if (drvdata->panic_notifier.notifier_call) {
> + ret = atomic_notifier_chain_register(&panic_notifier_list,
> + &drvdata->panic_notifier);
> + if (ret)
> + goto out;
> + }

When I review this patch, I recognize we can consolidate panic notifier
in coresight-tmc-core.c, so we don't need to distribute the changes
into ETF and ETR drivers (sorry if I misled you in my previous reply).

How about we change like below? We still can keep the panic_ops
callback, and then register a common callback tmc_panic_cb(), which
still checks device state and invoke device's sync callback.

diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c
index bd783c9dcb56..f7c175b3ae4c 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 +770,22 @@ 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;
+ int mode = coresight_get_mode(csdev);
+
+ if (mode == 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;
@@ -886,6 +903,12 @@ 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))
@@ -930,6 +953,10 @@ 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 {