From: Cristian Marussi cristian.marussi@arm.com
[ Upstream commit c7821c2d9c0dda0adf2bcf88e79b02a19a430be4 ]
When a protocol registers its events, the notification core takes care to rescan the hashtable of pending event handlers and activate all the possibly existent handlers referring to any of the events that are just registered by the new protocol. When a pending handler becomes active the core requests and enables the corresponding events in the SCMI firmware.
If, for whatever reason, the enable fails, such invalid event handler must be finally removed and freed. Let us ensure to use the scmi_put_active_handler() helper which handles properly the needed additional locking.
Failing to properly acquire all the needed mutexes exposes a race that leads to the following splat being observed:
WARNING: CPU: 0 PID: 388 at lib/refcount.c:28 refcount_warn_saturate+0xf8/0x148 Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Jun 30 2020 pstate: 40000005 (nZcv daif -PAN -UAO BTYPE=--) pc : refcount_warn_saturate+0xf8/0x148 lr : refcount_warn_saturate+0xf8/0x148 Call trace: refcount_warn_saturate+0xf8/0x148 scmi_put_handler_unlocked.isra.10+0x204/0x208 scmi_put_handler+0x50/0xa0 scmi_unregister_notifier+0x1bc/0x240 scmi_notify_tester_remove+0x4c/0x68 [dummy_scmi_consumer] scmi_dev_remove+0x54/0x68 device_release_driver_internal+0x114/0x1e8 driver_detach+0x58/0xe8 bus_remove_driver+0x88/0xe0 driver_unregister+0x38/0x68 scmi_driver_unregister+0x1c/0x28 scmi_drv_exit+0x1c/0xae0 [dummy_scmi_consumer] __arm64_sys_delete_module+0x1a4/0x268 el0_svc_common.constprop.3+0x94/0x178 do_el0_svc+0x2c/0x98 el0_sync_handler+0x148/0x1a8 el0_sync+0x158/0x180
Link: https://lore.kernel.org/r/20201013133109.49821-1-cristian.marussi@arm.com Fixes: e7c215f358a35 ("firmware: arm_scmi: Add notification callbacks-registration") Signed-off-by: Cristian Marussi cristian.marussi@arm.com Signed-off-by: Sudeep Holla sudeep.holla@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/firmware/arm_scmi/notify.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-)
diff --git a/drivers/firmware/arm_scmi/notify.c b/drivers/firmware/arm_scmi/notify.c index 4731daaacd19e..4d9f6de3a7fae 100644 --- a/drivers/firmware/arm_scmi/notify.c +++ b/drivers/firmware/arm_scmi/notify.c @@ -1403,15 +1403,21 @@ static void scmi_protocols_late_init(struct work_struct *work) "finalized PENDING handler - key:%X\n", hndl->key); ret = scmi_event_handler_enable_events(hndl); + if (ret) { + dev_dbg(ni->handle->dev, + "purging INVALID handler - key:%X\n", + hndl->key); + scmi_put_active_handler(ni, hndl); + } } else { ret = scmi_valid_pending_handler(ni, hndl); - } - if (ret) { - dev_dbg(ni->handle->dev, - "purging PENDING handler - key:%X\n", - hndl->key); - /* this hndl can be only a pending one */ - scmi_put_handler_unlocked(ni, hndl); + if (ret) { + dev_dbg(ni->handle->dev, + "purging PENDING handler - key:%X\n", + hndl->key); + /* this hndl can be only a pending one */ + scmi_put_handler_unlocked(ni, hndl); + } } } mutex_unlock(&ni->pending_mtx);