Re: [PATCH v3 09/19] unwind: Introduce sframe user space unwinding

[Josh Poimboeuf]

On Tue, Oct 29, 2024 at 02:27:09PM +0100, Peter Zijlstra wrote:
> > +int sframe_add_section(unsigned long sframe_addr, unsigned long text_start,
> > +		       unsigned long text_end)
> > +{
> > +	struct mm_struct *mm = current->mm;
> > +	struct vm_area_struct *sframe_vma;
> > +
> > +	mmap_read_lock(mm);
> 
> DEFINE_GUARD(mmap_read_lock, struct mm_struct *,
> 	     mmap_read_lock(_T), mmap_read_unlock(_T))
> 
> in include/linux/mmap_lock.h ?

Will do.

> > @@ -2784,6 +2785,16 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
> >  	case PR_RISCV_SET_ICACHE_FLUSH_CTX:
> >  		error = RISCV_SET_ICACHE_FLUSH_CTX(arg2, arg3);
> >  		break;
> > +	case PR_ADD_SFRAME:
> > +		if (arg5)
> > +			return -EINVAL;
> > +		error = sframe_add_section(arg2, arg3, arg4);
> > +		break;
> > +	case PR_REMOVE_SFRAME:
> > +		if (arg3 || arg4 || arg5)
> > +			return -EINVAL;
> > +		error = sframe_remove_section(arg2);
> > +		break;
> >  	default:
> >  		error = -EINVAL;
> >  		break;
> 
> So I realize that mtree has an internal lock, but are we sure we don't
> want a lock around those prctl()s?

Not that I can tell?  It relies on the mtree internal locking for
atomicity.

For sframe_remove_section() it uses srcu to delay the freeing until all
sframe_find()'s have completed.

-- 
Josh