2019-07-26 11:30:48

by Anders Roxell

Subject: [PATCH] iommu: arm-smmu-v3: Mark expected switch fall-through

When fall-through warnings was enabled by default, commit d93512ef0f0e
("Makefile: Globally enable fall-through warning"), the following
warning was starting to show up:

../drivers/iommu/arm-smmu-v3.c: In function ‘arm_smmu_write_strtab_ent’:
../drivers/iommu/arm-smmu-v3.c:1189:7: warning: this statement may fall
through [-Wimplicit-fallthrough=]
if (disable_bypass)
^
../drivers/iommu/arm-smmu-v3.c:1191:3: note: here
default:
^~~~~~~

Rework so that the compiler doesn't warn about fall-through. Make it
clearer by calling 'BUG()' when disable_bypass is set, and always
'break;'

Cc: [email protected] # v4.2+
Fixes: 5bc0a11664e1 ("iommu/arm-smmu: Don't BUG() if we find aborting STEs with disable_bypass")
Signed-off-by: Anders Roxell <[email protected]>
---
drivers/iommu/arm-smmu-v3.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index a9a9fabd3968..8e5f0565996d 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -1186,8 +1186,9 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
ste_live = true;
break;
case STRTAB_STE_0_CFG_ABORT:
- if (disable_bypass)
- break;
+ if (!disable_bypass)
+ BUG();
+ break;
default:
BUG(); /* STE corruption */
}
--
2.20.1

2019-07-26 12:07:37

by Robin Murphy

Subject: Re: [PATCH] iommu: arm-smmu-v3: Mark expected switch fall-through

On 26/07/2019 12:28, Anders Roxell wrote:
> When fall-through warnings was enabled by default, commit d93512ef0f0e

That commit ID only exists in a handful of old linux-next tags.

> ("Makefile: Globally enable fall-through warning"), the following
> warning was starting to show up:
>
> ../drivers/iommu/arm-smmu-v3.c: In function ‘arm_smmu_write_strtab_ent’:
> ../drivers/iommu/arm-smmu-v3.c:1189:7: warning: this statement may fall
> through [-Wimplicit-fallthrough=]
> if (disable_bypass)
> ^
> ../drivers/iommu/arm-smmu-v3.c:1191:3: note: here
> default:
> ^~~~~~~
>
> Rework so that the compiler doesn't warn about fall-through. Make it
> clearer by calling 'BUG()' when disable_bypass is set, and always
> 'break;'
>
> Cc: [email protected] # v4.2+
> Fixes: 5bc0a11664e1 ("iommu/arm-smmu: Don't BUG() if we find aborting STEs with disable_bypass")

Why? There's no actual bug, and not even current kernels have that
warning enabled.

> Signed-off-by: Anders Roxell <[email protected]>
> ---
> drivers/iommu/arm-smmu-v3.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index a9a9fabd3968..8e5f0565996d 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -1186,8 +1186,9 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
> ste_live = true;
> break;
> case STRTAB_STE_0_CFG_ABORT:
> - if (disable_bypass)
> - break;
> + if (!disable_bypass)
> + BUG();

You may as well just use BUG_ON().

Robin.

> + break;
> default:
> BUG(); /* STE corruption */
> }
>