Re: [PATCH 2/2] perf/tools: put new buildid locks to use

[Ingo Molnar <mingo@kernel.org>]

* Milos Vyletel <milos@redhat.com> wrote:

> On Thu, May 14, 2015 at 01:38:21PM +0200, Jiri Olsa wrote:
> 
> > On Thu, May 14, 2015 at 12:40:59PM +0200, Ingo Molnar wrote:
> > > 
> > > * Milos Vyletel <milos@redhat.com> wrote:
> > > 
> > > > Use new read/write locks when accesing buildid directory on places where
> > > > we may race if multiple instances are run simultaneously.
> > > 
> > > Dunno, this will create locking interaction between multiple instances 
> > > of perf - hanging each other, etc.
> > > 
> > > And it seems unnecessary: the buildid hierarchy is already spread out. 
> > > What kind of races might there be?
> > 
> > there was just recently one fixed by commit:
> >   0635b0f71424 perf tools: Fix race in build_id_cache__add_s()
> > 
> > havent checked the final patch yet, but the idea is to
> > protect us from similar bugs
> 
> right. on top of race with EEXIST couple more are possible (EMLINK, 
> ENOSPC, EDQUOT, ENOMEM... the only way to prevent them all is to 
> lock this kind of operations and make sure we run one at a time.

No, that's not the only way to avoid the race - see my previous mail.

Thanks,

	Ingo