Fwd: Re: [Outreachy kernel] Re: [PATCH] gpu: drm: Use list_first_entry instead of list_entry

From: Christian KÃnig
Date: Mon Mar 19 2018 - 09:18:21 EST

Forwarding to LKML once more because Outlook decided to change it to HTML mail.

Christian.

Am 19.03.2018 um 12:06 schrieb Julia Lawall:
On Mon, 19 Mar 2018, Christian KÃnig wrote:

Mhm, actually that patch isn't correct. What we grab get here is the next
entry, not the first one.

We don't have an alias list_next_entry for list_first_entry?
As compared to the semantic patch I proposed earlier today, it would seem
that list_first_entry is useful when the types are different? One would
have to check the result of course, but a list eleemnt with the same type
as the structure that contains the list might be unlikely?

The list element and the list head have different types in this case:
if (sa_manager->hole->next == &sa_manager->olist)
return;
- sa_bo = list_entry(sa_manager->hole->next, struct amdgpu_sa_bo, olist);
+ sa_bo = list_first_entry(sa_manager->hole, struct amdgpu_sa_bo, olist);

sa_manager->olist is the head of the list and sa_manager->hole can point to both the head and any element in the list.

The statement "if (sa_manager->hole->next == &sa_manager->olist)" now checks if the next pointer points to the head and if so aborts the function.

Then the statement "sa_bo = list_entry(sa_manager->hole->next, struct amdgpu_sa_bo, olist);" returns the next element after the hole to try to release it.

So with the automated change the code is still correct, but NOT easier to understand because we actually don't grab the first element here.

Regards,
Christian.

julia

Regards,
Christian.

Am 18.03.2018 um 22:51 schrieb Arushi Singhal:
This patch replaces list_entry with list_first_entry as it makes the
code more clear.
Done using coccinelle:

@@
expression e;
@@
(
- list_entry(e->next,
+ list_first_entry(e,
...)
|
- list_entry(e->prev,
+ list_last_entry(e,
...)
)

Signed-off-by: Arushi Singhal<arushisinghal19971997@xxxxxxxxx>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_sa.c | 4 ++--
drivers/gpu/drm/omapdrm/dss/display.c | 4 ++--
drivers/gpu/drm/radeon/radeon_sa.c | 4 ++--
3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_sa.c
b/drivers/gpu/drm/amd/amdgpu/amdgpu_sa.c
index 3144400..646f593 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_sa.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_sa.c
@@ -158,7 +158,7 @@ static void amdgpu_sa_bo_try_free(struct
amdgpu_sa_manager *sa_manager)
if (sa_manager->hole->next == &sa_manager->olist)
return;
- sa_bo = list_entry(sa_manager->hole->next, struct amdgpu_sa_bo,
olist);
+ sa_bo = list_first_entry(sa_manager->hole, struct amdgpu_sa_bo,
olist);
list_for_each_entry_safe_from(sa_bo, tmp, &sa_manager->olist, olist) {
if (sa_bo->fence == NULL ||
!dma_fence_is_signaled(sa_bo->fence)) {
@@ -183,7 +183,7 @@ static inline unsigned amdgpu_sa_bo_hole_eoffset(struct
amdgpu_sa_manager *sa_ma
struct list_head *hole = sa_manager->hole;
if (hole->next != &sa_manager->olist) {
- return list_entry(hole->next, struct amdgpu_sa_bo,
olist)->soffset;
+ return list_first_entry(hole, struct amdgpu_sa_bo,
olist)->soffset;
}
return sa_manager->size;
}
diff --git a/drivers/gpu/drm/omapdrm/dss/display.c
b/drivers/gpu/drm/omapdrm/dss/display.c
index 0c9480b..fb9ecae 100644
--- a/drivers/gpu/drm/omapdrm/dss/display.c
+++ b/drivers/gpu/drm/omapdrm/dss/display.c
@@ -158,8 +158,8 @@ struct omap_dss_device *omap_dss_get_next_device(struct
omap_dss_device *from)
goto out;
}
- dssdev = list_entry(l->next, struct omap_dss_device,
- panel_list);
+ dssdev = list_first_entry(l, struct omap_dss_device,
+ panel_list);
omap_dss_get_device(dssdev);
goto out;
}
diff --git a/drivers/gpu/drm/radeon/radeon_sa.c
b/drivers/gpu/drm/radeon/radeon_sa.c
index 197b157..66c0482 100644
--- a/drivers/gpu/drm/radeon/radeon_sa.c
+++ b/drivers/gpu/drm/radeon/radeon_sa.c
@@ -158,7 +158,7 @@ static void radeon_sa_bo_try_free(struct
radeon_sa_manager *sa_manager)
if (sa_manager->hole->next == &sa_manager->olist)
return;
- sa_bo = list_entry(sa_manager->hole->next, struct radeon_sa_bo,
olist);
+ sa_bo = list_first_entry(sa_manager->hole, struct radeon_sa_bo,
olist);
list_for_each_entry_safe_from(sa_bo, tmp, &sa_manager->olist, olist) {
if (sa_bo->fence == NULL ||
!radeon_fence_signaled(sa_bo->fence)) {
return;
@@ -182,7 +182,7 @@ static inline unsigned radeon_sa_bo_hole_eoffset(struct
radeon_sa_manager *sa_ma
struct list_head *hole = sa_manager->hole;
if (hole->next != &sa_manager->olist) {
- return list_entry(hole->next, struct radeon_sa_bo,
olist)->soffset;
+ return list_first_entry(hole, struct radeon_sa_bo,
olist)->soffset;
}
return sa_manager->size;
}
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