Re: [PATCH v15 03/15] accel/rocket: wait for a running IRQ handler before resetting a core

["Heiko Stübner" <heiko@sntech.de>]

Am Sonntag, 1. November 2026, 09:22:55 Mitteleuropäische Normalzeit schrieb Jiaxing Hu:
> drm_sched_stop() does not wait for a threaded handler that is already
> running. Call synchronize_irq() after it, outside job_lock, which the
> handler takes.
> 
> Before the sync, mask the block's interrupt and clear its raw status, so
> that an active core cannot signal a completion after it. Do that under
> job_lock, since rocket_job_hw_submit() arms the same mask under that lock,
> and only when pm_runtime_get_if_active() returns a positive count: the
> reset holds no runtime PM reference, and with the domain down a register
> access takes an async SError.
> 
> Igor Paunovic's induced-reset runs on RK3588, including a two-task job that
> puts hw_submit() on the IRQ thread, found no fault; as he put it, "this
> does not show the race is closed".
> 
> Link: https://lore.kernel.org/all/20260819073530.6087-1-royalnet026@gmail.com/
> Link: https://lore.kernel.org/all/CAEWPSH5mxTbUkNouxm6yecMZYvDowquhvYvhaXQ8HoMtHD5U1g@mail.gmail.com/
> Link: https://lore.kernel.org/all/20260912113717.6819-1-royalnet026@gmail.com/
> Link: https://lore.kernel.org/all/20260916132824.13527-1-royalnet026@gmail.com/
> Link: https://lore.kernel.org/all/20260919103422.148834-1-royalnet026@gmail.com/
> Suggested-by: Igor Paunovic <royalnet026@gmail.com>
> Signed-off-by: Jiaxing Hu <gahing@gahingwoo.com>
> Tested-by: Igor Paunovic <royalnet026@gmail.com> # RK3588, three cores, induced reset, JOB_TIMEOUT_MS=2
> ---
>  drivers/accel/rocket/rocket_job.c | 71 +++++++++++++++++++++++++++++--
>  1 file changed, 68 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/accel/rocket/rocket_job.c b/drivers/accel/rocket/rocket_job.c
> index 03e5f094f60b..5b2abf40b618 100644
> --- a/drivers/accel/rocket/rocket_job.c
> +++ b/drivers/accel/rocket/rocket_job.c
> @@ -401,9 +401,74 @@ rocket_reset(struct rocket_core *core, struct drm_sched_job *bad)
>  	drm_sched_stop(&core->sched, bad);
>  
>  	/*
> -	 * Remaining interrupts have been handled, but we might still have
> -	 * stuck jobs. Let's make sure the PM counters stay balanced by
> -	 * manually calling pm_runtime_put_noidle().
> +	 * Mask the block before waiting. hw_submit() arms INTERRUPT_MASK on
> +	 * every submit and only the hardirq clears it, so on an ordinary
> +	 * timeout it is still live and a completion can arrive after the sync
> +	 * returns. The next submit re-arms it, so nothing is lost here.
> +	 *
> +	 * Only when the device is already awake, though. This function holds no
> +	 * runtime PM reference of its own: the only one in the window belongs to
> +	 * in_flight_job, and the completion path may have put it and cleared the
> +	 * pointer before the timeout worker got here. drm_sched_stop() above can
> +	 * block for a long time, and it drops every pending job's credits, so
> +	 * rocket_job_is_idle() is true and nothing keeps the core resumed. On
> +	 * this hardware a register access with the domain down takes an async
> +	 * SError, so a reset must not be the thing that causes one.
> +	 *
> +	 * Only a positive answer will do. pm_runtime_get_if_active() tests
> +	 * power.disable_depth before power.runtime_status, so -EINVAL MASKS a
> +	 * suspended device rather than excluding one: pm_runtime_force_suspend(),
> +	 * which is this driver's own system suspend callback, disables runtime PM
> +	 * first and turns the clocks off second, and rocket_core_fini() suspends
> +	 * the core and disables before it cancels the timeout worker. Both leave
> +	 * the domain down with -EINVAL on offer.
> +	 *
> +	 * The cost is the other half of that ambiguity. A core that is still up
> +	 * with runtime PM disabled (pm_runtime_force_suspend() before its
> +	 * callback has run, or CONFIG_PM=n under COMPILE_TEST) is left unmasked,
> +	 * because writing to it would mean writing to the half that is down as
> +	 * well.
> +	 *
> +	 * Clear the raw status along with the mask, the way the completion path
> +	 * does. Masking alone leaves the DPU bit latched until
> +	 * rocket_core_reset(), and the hardirq decides on raw status alone, so a
> +	 * fault from the IOMMU that shares this line would wake the thread again
> +	 * and what the comment below asserts would stop being true.
> +	 *
> +	 * UNDER job_lock, because rocket_job_hw_submit() arms this same
> +	 * register and always runs under that lock. reset.pending is set here
> +	 * without the lock and read there with it, so a submit that has already
> +	 * passed its check can re-arm the mask after this clears it, and then
> +	 * the synchronize_irq() below fences a handler that is no longer the
> +	 * one that matters: the block is left running a task with its
> +	 * interrupt live. rocket_job_handle_irq() avoids the same race on
> +	 * OPERATION_ENABLE by making its completion writes under this lock.
> +	 *
> +	 * pm_runtime_get_if_active() does not invoke a callback -- it only
> +	 * takes a reference on an already-active device -- and
> +	 * pm_runtime_put_autosuspend() is asynchronous, so neither can re-enter
> +	 * this driver's runtime PM callbacks while the lock is held.

This can be way short please, the wall of text is very hard to read.

> +	 */
> +	scoped_guard(mutex, &core->job_lock) {
> +		if (pm_runtime_get_if_active(core->dev) > 0) {
> +			rocket_pc_writel(core, INTERRUPT_MASK, 0x0);
> +			rocket_pc_writel(core, INTERRUPT_CLEAR, 0x1ffff);
> +			pm_runtime_put_autosuspend(core->dev);
> +		}
> +	}
> +
> +	/*
> +	 * drm_sched_stop() returns without waiting for a threaded handler that
> +	 * is already running, so wait for one here. This has to stay outside
> +	 * job_lock: the handler takes that lock, so waiting for it while
> +	 * holding it would deadlock instead of fencing anything.
> +	 */
> +	synchronize_irq(core->irq);
> +
> +	/*
> +	 * No handler is running now, but we might still have stuck jobs. Let's
> +	 * make sure the PM counters stay balanced by manually calling
> +	 * pm_runtime_put_noidle().
>  	 */
>  	scoped_guard(mutex, &core->job_lock) {
>  		if (core->in_flight_job)
>