Re: [PATCH V4 17/18] amdkfd: set_debug_trap ioctl only works on a primary kfd_process target

["Kuehling, Felix" <felix.kuehling@amd.com>]

On 2025-09-23 03:26, Zhu Lingshan wrote:
> The user space program pass down a pid to kfd
> through set_debug_trap ioctl, which can help
> find the corresponding user space program and
> its mm struct.
>
> However, these information is insufficient to
> locate a specific kfd process among the
> multiple kfd_process that belong to the
> same user space program.
>
> For correctness and backward compatibilities,
> this commit only allow set_debut_trap ioctl
> work for a user space program which does not
> own any secondary kfd_process.

What happens if a secondary context is created after the debugger 
attaches to a process?

It may be simpler and more consistent to allow debugging of the primary 
context, even if secondary contexts exist. Just ignore any secondary 
contexts for the purpose of the debug API.

Regards,
   Felix


>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@amd.com>
> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_chardev.c | 29 ++++++++++++++++++++++++
>   1 file changed, 29 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c b/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
> index 662b181f1fd2..2df095e25c2e 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
> @@ -36,6 +36,7 @@
>   #include <linux/ptrace.h>
>   #include <linux/dma-buf.h>
>   #include <linux/processor.h>
> +#include <linux/fdtable.h>
>   #include "kfd_priv.h"
>   #include "kfd_device_queue_manager.h"
>   #include "kfd_svm.h"
> @@ -2918,6 +2919,25 @@ static int kfd_ioctl_runtime_enable(struct file *filep, struct kfd_process *p, v
>   	return r;
>   }
>   
> +static int kfd_process_count_cb(const void *num, struct file *filep, unsigned int n)
> +{
> +	u16 *ret = (u16 *)num;
> +
> +	if (filep->f_op == &kfd_fops)
> +		(*ret)++;
> +
> +	return 0;
> +}
> +
> +static u16 kfd_process_count(struct task_struct *thread)
> +{
> +	u16 count = 0;
> +
> +	iterate_fd(thread->files, 0, kfd_process_count_cb, (const void *)&count);
> +
> +	return count;
> +}
> +
>   static int kfd_ioctl_set_debug_trap(struct file *filep, struct kfd_process *p, void *data)
>   {
>   	struct kfd_ioctl_dbg_trap_args *args = data;
> @@ -2927,6 +2947,7 @@ static int kfd_ioctl_set_debug_trap(struct file *filep, struct kfd_process *p, v
>   	struct kfd_process *target = NULL;
>   	struct kfd_process_device *pdd = NULL;
>   	int r = 0;
> +	u16 process_count = 0;
>   
>   	if (sched_policy == KFD_SCHED_POLICY_NO_HWS) {
>   		pr_err("Debugging does not support sched_policy %i", sched_policy);
> @@ -2984,6 +3005,14 @@ static int kfd_ioctl_set_debug_trap(struct file *filep, struct kfd_process *p, v
>   	if (r)
>   		goto out;
>   
> +	process_count = kfd_process_count(thread);
> +	/* The user space program has secondary contexts */
> +	if (process_count > 1) {
> +		pr_err("Detect multiple kfd_process owned by PID %i, please consider close any secondary kfd_process and try again\n", args->pid);
> +		r = -EINVAL;
> +		goto out;
> +	}
> +
>   	mutex_lock(&target->mutex);
>   
>   	if (args->op != KFD_IOC_DBG_TRAP_ENABLE && !target->debug_trap_enabled) {