Re: [PATCH 4/6] powerpc: book3s: vas: use lock guard for mutex

[Shrikanth Hegde]

On 3/14/25 13:55, Peter Zijlstra wrote:
> On Fri, Mar 14, 2025 at 11:15:42AM +0530, Shrikanth Hegde wrote:
> > use guard(mutex) for scope based resource management of mutex.
> > This would make the code simpler and easier to maintain.
> >
> > More details on lock guards can be found at
> > https://lore.kernel.org/all/20230612093537.614161713@xxxxxxxxxxxxx/T/#u
> >
> > There is also an example of using scoped_guard.
> >
> > Signed-off-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
> > ---
> >   arch/powerpc/platforms/book3s/vas-api.c | 19 ++++++-------------
> >   1 file changed, 6 insertions(+), 13 deletions(-)
> >
> > diff --git a/arch/powerpc/platforms/book3s/vas-api.c b/arch/powerpc/platforms/book3s/vas-api.c
> > index 0b6365d85d11..eb1a97271afb 100644
> > --- a/arch/powerpc/platforms/book3s/vas-api.c
> > +++ b/arch/powerpc/platforms/book3s/vas-api.c
> > @@ -425,7 +425,7 @@ static vm_fault_t vas_mmap_fault(struct vm_fault *vmf)
> >   		return VM_FAULT_SIGBUS;
> >   	}
> >   
> > -	mutex_lock(&txwin->task_ref.mmap_mutex);
> > +	guard(mutex)(&txwin->task_ref.mmap_mutex);
> >   	/*
> >   	 * The window may be inactive due to lost credit (Ex: core
> >   	 * removal with DLPAR). If the window is active again when
> > @@ -437,11 +437,9 @@ static vm_fault_t vas_mmap_fault(struct vm_fault *vmf)
> >   		if (paste_addr) {
> >   			fault = vmf_insert_pfn(vma, vma->vm_start,
> >   					(paste_addr >> PAGE_SHIFT));
> > -			mutex_unlock(&txwin->task_ref.mmap_mutex);
> >   			return fault;
> >   		}
> >   	}
> > -	mutex_unlock(&txwin->task_ref.mmap_mutex);
>
> I had to open up this file to check, but this seems incorrect since you
> now also run do_fail_paste() with the lock held, where previously you
> did not.

Yes. Got it. let me use scoped_guard for it as well. There is get_user 
and other things in the fail parse and having it with mutex will not be 
good.

I went through the rest of the patches too. It is mostly return after 
mutex.

Only in Patch 5/6 there is additional debug statement. Let me put a 
comment there.

> >   	/*
> >   	 * Received this fault due to closing the actual window.