On Mon, Sep 28, 2020 at 02:44:57PM +0200, Lukas Bulwahn wrote:
> Commit b6724f118d44 ("prctl: Hook L1D flushing in via prctl") checks the
> validity for enable_l1d_flush_for_task() and introduces some superfluous
> local variables for that implementation.
>
> make clang-analyzer on x86_64 tinyconfig caught my attention with:
>
> arch/x86/mm/tlb.c:332:2: warning: Value stored to 'cpu' is never read \
> [clang-analyzer-deadcode.DeadStores]
>
> Compilers will detect these superfluous local variables and assignment and
> optimize this anyway. So, the resulting binary is identical before and
> after this change.
>
> Simplify the code and remove superfluous local variables to make
> clang-analyzer happy.
>
> No functional change. No change in binary with supported compilers.
>
> Signed-off-by: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx>
> ---
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> applies cleanly on next-20200925
>
> Balbir, please review and ack.
> Thomas, please pick this minor non-urgent clean-up patch into the x86/pti
> branch of tip as follow-up to:
> https://lore.kernel.org/lkml/160026187842.15536.285514864386042510.tip-bot2@tip-bot2/
>
> I quickly confirmed that the binary did not change with this change to the
> source code; The hash of tlb.o remained the same before and after the change.
>
> So, in my setup:
> md5sum tlb.o
> 7c7e096bab0fd87bd2c8437d8c7dc3fa tlb.o
>
> linux-safety, please verify and validate this change.
>
> arch/x86/mm/tlb.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index 6b0f4c88b07c..90515c04d90a 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -316,7 +316,7 @@ EXPORT_SYMBOL_GPL(leave_mm);
>
> int enable_l1d_flush_for_task(struct task_struct *tsk)
> {
> - int cpu, ret = 0, i;
> + int i;
>
> /*
> * Do not enable L1D_FLUSH_OUT if
> @@ -329,7 +329,7 @@ int enable_l1d_flush_for_task(struct task_struct *tsk)
> !static_cpu_has(X86_FEATURE_FLUSH_L1D))
> return -EINVAL;
>
> - cpu = get_cpu();
> + get_cpu();
>
> for_each_cpu(i, &tsk->cpus_mask) {
> if (cpu_data(i).smt_active == true) {
> @@ -340,7 +340,7 @@ int enable_l1d_flush_for_task(struct task_struct *tsk)
>
> set_ti_thread_flag(&tsk->thread_info, TIF_SPEC_L1D_FLUSH);
> put_cpu();
> - return ret;
> + return 0;
> }
>
> int disable_l1d_flush_for_task(struct task_struct *tsk)
> --
> 2.17.1
>
