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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Sep 2025 04:31:27.4157 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 7728036a-3b7f-477d-a6a3-08ddf27e67a3 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AM2PEPF0001C717.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM7PR08MB5336 Hi, > > Hi, > > > >> Hi Sean, > >> > >> On Thu, Sep 11, 2025 at 11:33:15AM -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 will cause a deadlock > >> > if a panic occurs while one of the other coresight functions that uses > >> > bus_for_each_dev is running. > >> > >> The decription is a bit misleading. Even when IRQ is disabled, if an > >> exception happens, a CPU still can be trapped for handling kernel panic. > >> > >> > Maintain a separate list of coresight devices to access during a panic. > >> > >> Rather than maintaining a separate list and introducing a new spinlock, > >> I would argue if we can simply register panic notifier in TMC ETR and > >> ETF drviers (see tmc_panic_sync_etr() and tmc_panic_sync_etf()). > >> > >> If there is no dependency between CoreSight modules in panic sync flow, > >> it is not necessary to maintain list (and lock) for these modules. > > Yeah, I was thinking about this as I was preparing v2 of this patch. > > > +1 for this. > > and using the spinlock in the panic_cb doesn't work on PREEMPT_RT side. > > What do you mean by this? I am using lockdep and it did not warn about this, > so I assume that on PREEMPT_RT IRQs remain enabled in this path. Hmm, I don't believe this. When you see the panic(), it explicitly disable irq. and preempt_disabled() before calling atomic_notifier_call_chain(&panic_notifier_list, 0, buf); also, atomic_nofier_call_chain() is rcu critical section. As you know, since the spinlock becomes sleepable lock in PREEMPT_RT this is problem. The reason why lockdep doesn't report this problem since it was disabled before panic notifier chain by calling debug_locks_off(); Thanks. -- Sincerely, Yeoreum Yun