[Intel-xe] [PATCH 2/2] drm/xe: Handle -EDEADLK case in exec ioctl

[Hellstrom, Thomas]

On Mon, 2023-05-08 at 22:24 -0700, Niranjana Vishwanathapura wrote:
> With multiple active VMs, under memory pressure, it is possible that
> ttm_bo_validate() run into -EDEADLK in ttm_mem_evict_wait_busy() and
> return -ENOMEM.
> 
> Until ttm properly handles locking in such scenarios, best thing the
> driver can do is unwind the lock and retry.
> 
> Update xe_exec_begin to retry validating BOs with a timeout upon
> -ENOMEM.
> 
> Signed-off-by: Niranjana Vishwanathapura
> <niranjana.vishwanathapura at intel.com>
> ---
>  drivers/gpu/drm/xe/xe_exec.c | 27 ++++++++++++++++++++++++---
>  1 file changed, 24 insertions(+), 3 deletions(-)
Reviewed-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>

> 
> diff --git a/drivers/gpu/drm/xe/xe_exec.c
> b/drivers/gpu/drm/xe/xe_exec.c
> index ea869f2452ef..3db1b159586e 100644
> --- a/drivers/gpu/drm/xe/xe_exec.c
> +++ b/drivers/gpu/drm/xe/xe_exec.c
> @@ -8,6 +8,7 @@
>  #include <drm/drm_device.h>
>  #include <drm/drm_file.h>
>  #include <drm/xe_drm.h>
> +#include <linux/delay.h>
>  
>  #include "xe_bo.h"
>  #include "xe_device.h"
> @@ -91,6 +92,8 @@
>   *     Unlock all
>   */
>  
> +#define XE_EXEC_BIND_RETRY_TIMEOUT_MS 1000
> +
>  static int xe_exec_begin(struct xe_engine *e, struct ww_acquire_ctx
> *ww,
>                          struct ttm_validate_buffer tv_onstack[],
>                          struct ttm_validate_buffer **tv,
> @@ -99,12 +102,14 @@ static int xe_exec_begin(struct xe_engine *e,
> struct ww_acquire_ctx *ww,
>         struct xe_vm *vm = e->vm;
>         struct xe_vma *vma;
>         LIST_HEAD(dups);
> -       int err;
> +       ktime_t end = 0;
> +       int err = 0;
>  
>         *tv = NULL;
>         if (xe_vm_no_dma_fences(e->vm))
>                 return 0;
>  
> +retry:
>         err = xe_vm_lock_dma_resv(vm, ww, tv_onstack, tv, objs, true,
> 1);
>         if (err)
>                 return err;
> @@ -122,11 +127,27 @@ static int xe_exec_begin(struct xe_engine *e,
> struct ww_acquire_ctx *ww,
>                 if (err) {
>                         xe_vm_unlock_dma_resv(vm, tv_onstack, *tv,
> ww, objs);
>                         *tv = NULL;
> -                       return err;
> +                       break;
> +               }
> +       }
> +
> +       /*
> +        * With multiple active VMs, under memory pressure, it is
> possible that
> +        * ttm_bo_validate() run into -EDEADLK and in such case
> returns -ENOMEM.
> +        * Until ttm properly handles locking in such scenarios, best
> thing the
> +        * driver can do is retry with a timeout.
> +        */
> +       if (err == -ENOMEM) {
> +               ktime_t cur = ktime_get();
> +
> +               end = end ? : ktime_add_ms(cur,
> XE_EXEC_BIND_RETRY_TIMEOUT_MS);
> +               if (ktime_before(cur, end)) {
> +                       msleep(20);
> +                       goto retry;
>                 }
>         }
>  
> -       return 0;
> +       return err;
>  }
>  
>  static void xe_exec_end(struct xe_engine *e,