Re: [PATCH v7 02/16] arm64: Use update{,_tsk}_thread_flag()

[Dave Martin <Dave.Martin@arm.com>]

On Wed, May 09, 2018 at 05:17:28PM +0100, Will Deacon wrote:
> Hi Dave,
> 
> On Wed, May 09, 2018 at 05:12:51PM +0100, Dave Martin wrote:
> > This patch uses the new update_thread_flag() helpers to simplify a
> > couple of if () set; else clear; constructs.
> > 
> > No functional change.
> > 
> > Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> > Acked-by: Marc Zyngier <marc.zyngier@arm.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Will Deacon <will.deacon@arm.com>
> > ---
> >  arch/arm64/kernel/fpsimd.c | 19 +++++++------------
> >  1 file changed, 7 insertions(+), 12 deletions(-)
> > 
> > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> > index 87a3536..0c4e7e0 100644
> > --- a/arch/arm64/kernel/fpsimd.c
> > +++ b/arch/arm64/kernel/fpsimd.c

[...]

> > @@ -902,7 +900,7 @@ void fpsimd_thread_switch(struct task_struct *next)
> >  	if (current->mm)
> >  		task_fpsimd_save();
> >  
> > -	if (next->mm) {
> > +	if (next->mm)
> >  		/*
> >  		 * If we are switching to a task whose most recent userland
> >  		 * FPSIMD state is already in the registers of *this* cpu,
> > @@ -910,13 +908,10 @@ void fpsimd_thread_switch(struct task_struct *next)
> >  		 * the TIF_FOREIGN_FPSTATE flag so the state will be loaded
> >  		 * upon the next return to userland.
> >  		 */
> > -		if (__this_cpu_read(fpsimd_last_state.st) ==
> > -			&next->thread.uw.fpsimd_state
> > -		    && next->thread.fpsimd_cpu == smp_processor_id())
> > -			clear_tsk_thread_flag(next, TIF_FOREIGN_FPSTATE);
> > -		else
> > -			set_tsk_thread_flag(next, TIF_FOREIGN_FPSTATE);
> > -	}
> > +		update_tsk_thread_flag(next, TIF_FOREIGN_FPSTATE,
> > +			__this_cpu_read(fpsimd_last_state.st) !=
> > +				&next->thread.uw.fpsimd_state ||
> > +			next->thread.fpsimd_cpu != smp_processor_id());
> 
> Given the multi-line comment and this multi-line call, I'd be inclined to
> leave the curlies in place and then use a local bool for the complex
> condition.

Hey, curlies cost money, you know.

> With that:
> 
> Acked-by: Will Deacon <will.deacon@arm.com>

Are you content to see this merged without the change?  It doesn't seem
worth a respin of the whole series just for this.  I agree the code
would be clearer, but this patch doesn't actually make it worse IMHO.

If I respin for some reason though, I can address this and add your Ack.

Cheers
---Dave