show_cpu_pool_hog() only prints workers whose task is currently running on the CPU (task_is_running()). This misses workers that are busy processing a work item but are sleeping or blocked — for example, a worker that clears PF_WQ_WORKER and enters wait_event_idle(). Such a worker still occupies a pool slot and prevents progress, yet produces an empty backtrace section in the watchdog output. This is happening on real arm64 systems, where toggle_allocation_gate() IPIs every single CPU in the machine (which lacks NMI), causing workqueue stalls that show empty backtraces because toggle_allocation_gate() is sleeping in wait_event_idle(). Remove the task_is_running() filter so every in-flight worker in the pool's busy_hash is dumped. The busy_hash is protected by pool->lock, which is already held.
Unified · Split
| @@ -7583,9 +7583,9 @@ MODULE_PARM_DESC(panic_on_stall_time, "Panic if stall exceeds this many seconds · 7582 unmodified lines | ||
| 7583 | 7583 | |
| 7584 | 7584 | /* |
| 7585 | 7585 | * Show workers that might prevent the processing of pending work items. |
| 7586 | − * The only candidates are CPU-bound workers in the running state. | |
| 7587 | − * Pending work items should be handled by another idle worker | |
| 7588 | − * in all other situations. | |
| 7586 | + * A busy worker that is not running on the CPU (e.g. sleeping in | |
| 7587 | + * wait_event_idle() with PF_WQ_WORKER cleared) can stall the pool just as | |
| 7588 | + * effectively as a CPU-bound one, so dump every in-flight worker. | |
| 7589 | 7589 | */ |
| 7590 | 7590 | static void show_cpu_pool_hog(struct worker_pool *pool) |
| 7591 | 7591 | { |
| @@ -7596,19 +7596,17 @@ static void show_cpu_pool_hog(struct worker_pool *pool) · 4 unmodified lines | ||
| 7596 | 7596 | raw_spin_lock_irqsave(&pool->lock, irq_flags); |
| 7597 | 7597 | |
| 7598 | 7598 | hash_for_each(pool->busy_hash, bkt, worker, hentry) { |
| 7599 | − if (task_is_running(worker->task)) { | |
| 7600 | − /* | |
| 7601 | − * Defer printing to avoid deadlocks in console | |
| 7602 | − * drivers that queue work while holding locks | |
| 7603 | − * also taken in their write paths. | |
| 7604 | − */ | |
| 7605 | − printk_deferred_enter(); | |
| 7599 | + /* | |
| 7600 | + * Defer printing to avoid deadlocks in console | |
| 7601 | + * drivers that queue work while holding locks | |
| 7602 | + * also taken in their write paths. | |
| 7603 | + */ | |
| 7604 | + printk_deferred_enter(); | |
| 7606 | 7605 | |
| 7607 | − pr_info("pool %d:\n", pool->id); | |
| 7608 | − sched_show_task(worker->task); | |
| 7606 | + pr_info("pool %d:\n", pool->id); | |
| 7607 | + sched_show_task(worker->task); | |
| 7609 | 7608 | |
| 7610 | − printk_deferred_exit(); | |
| 7611 | − } | |
| 7609 | + printk_deferred_exit(); | |
| 7612 | 7610 | } |
| 7613 | 7611 | |
| 7614 | 7612 | raw_spin_unlock_irqrestore(&pool->lock, irq_flags); |
| @@ -7619,7 +7617,7 @@ static void show_cpu_pools_hogs(void) · 4 unmodified lines | ||
| 7619 | 7617 | struct worker_pool *pool; |
| 7620 | 7618 | int pi; |
| 7621 | 7619 | |
| 7622 | − pr_info("Showing backtraces of running workers in stalled CPU-bound worker pools:\n"); | |
| 7620 | + pr_info("Showing backtraces of busy workers in stalled CPU-bound worker pools:\n"); | |
| 7623 | 7621 | |
| 7624 | 7622 | rcu_read_lock(); |
| 7625 | 7623 | |