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

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Message-ID: <20241029165018.r4l5wix24s3f22c6@treble.attlocal.net>
Date: Tue, 29 Oct 2024 09:50:18 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, Indu Bhagat <indu.bhagat@...cle.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
	linux-toolchains@...r.kernel.org, Jordan Rome <jordalgo@...a.com>,
	Sam James <sam@...too.org>, linux-trace-kernel@...r.kerne.org,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	Jens Remus <jremus@...ux.ibm.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Florian Weimer <fweimer@...hat.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v3 09/19] unwind: Introduce sframe user space unwinding

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