Re: [PATCH] fix race in AF_UNIX

[David Miller <davem@davemloft.net>]

From: Miklos Szeredi <miklos@szeredi.hu>
Date: Wed, 06 Jun 2007 10:08:29 +0200

> > > > Holding a global mutex over recvmsg() calls under AF_UNIX is pretty
> > > > much a non-starter, this will kill performance for multi-threaded
> > > > apps.
> > > 
> > > That's an rwsem held for read.  It's held for write in unix_gc() only
> > > for a short duration, and unix_gc() should only rarely be called.  So
> > > I don't think there's any performance problem here.
> > 
> > It pulls a non-local cacheline into the local thread, that's extremely
> > expensive on SMP.
> 
> OK, here's an updated patch, that uses ->readlock, and passes my
> testing.

Thanks a lot, I'll review this as soon as possible unless
someone else beats me to it :)