Re: [PATCH] drm/i915: Ditch the i915_gem_ww_ctx loop member

On Mon, 16 Aug 2021 at 09:49, Thomas Hellström thomas.hellstrom@linux.intel.com wrote:

It's only used by the for_i915_gem_ww() macro and we can use the (typically) on-stack _err variable in its place.

While initially setting the _err variable to -EDEADLK to enter the loop, we clear it before actually entering using fetch_and_zero() to avoid empty loops or code not setting the _err variable running forever.

Suggested-by: Maarten Lankhorst maarten.lankhorst@linux.intel.com Signed-off-by: Thomas Hellström thomas.hellstrom@linux.intel.com

---

drivers/gpu/drm/i915/i915_gem_ww.h | 23 ++++++++--------------- 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_ww.h b/drivers/gpu/drm/i915/i915_gem_ww.h index f6b1a796667b..98348b1e6182 100644 --- a/drivers/gpu/drm/i915/i915_gem_ww.h +++ b/drivers/gpu/drm/i915/i915_gem_ww.h @@ -7,12 +7,13 @@

#include <drm/drm_drv.h>

+#include "i915_utils.h"

struct i915_gem_ww_ctx { struct ww_acquire_ctx ctx; struct list_head obj_list; struct drm_i915_gem_object *contended;

•   unsigned short intr;
  

•   unsigned short loop;
  

•   bool intr;
  

};

void i915_gem_ww_ctx_init(struct i915_gem_ww_ctx *ctx, bool intr); @@ -23,28 +24,20 @@ void i915_gem_ww_unlock_single(struct drm_i915_gem_object *obj); /* Internal functions used by the inlines! Don't use. */ static inline int __i915_gem_ww_fini(struct i915_gem_ww_ctx *ww, int err) {

•   ww->loop = 0;
    if (err == -EDEADLK) {
            err = i915_gem_ww_ctx_backoff(ww);
            if (!err)
  

•                   ww->loop = 1;
  

•                   err = -EDEADLK;
    }
  
  

•   if (!ww->loop)
  

•   if (err != -EDEADLK)
            i915_gem_ww_ctx_fini(ww);
  
    return err;
  

}

-static inline void -__i915_gem_ww_init(struct i915_gem_ww_ctx *ww, bool intr) -{

•   i915_gem_ww_ctx_init(ww, intr);
  

•   ww->loop = 1;
  

-}

-#define for_i915_gem_ww(_ww, _err, _intr) \

•   for (__i915_gem_ww_init(_ww, _intr); (_ww)->loop;       \
  

+#define for_i915_gem_ww(_ww, _err, _intr) \

•   for (i915_gem_ww_ctx_init(_ww, _intr), (_err) = -EDEADLK; \
  

•        fetch_and_zero(&_err) == -EDEADLK;                   \
  

Doesn't this now hide "normal" errors, like say get_pages() returning -ENOSPC or so?

         _err = __i915_gem_ww_fini(_ww, _err))

#endif

2.31.1