On 8/16/21 3:25 PM, Matthew Auld wrote:

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?

Yes, good catch. We should either just clear the -EDEADLK case, or not clear the error at all..

/Thomas

On 8/16/21 3:34 PM, Maarten Lankhorst wrote:

Op 16-08-2021 om 15:30 schreef Thomas Hellström:

...

On 8/16/21 3:25 PM, Matthew Auld wrote:

...

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?

Yes, good catch. We should either just clear the -EDEADLK case, or not clear the error at all..

/Thomas

I believe not setting _err is a bug anyway. Why would you do such a loop without at least one err = ww_mutex_lock(&ww); ?

Infinite loop would catch that at first test.

OK, I'll skip the clearing then.

/Thomas

~Maarten