----- Original Message ----- > From: "Steven Rostedt" <rost...@goodmis.org> > To: "Peter Zijlstra" <pet...@infradead.org> > Cc: "Mathieu Desnoyers" <mathieu.desnoy...@efficios.com>, > linux-kernel@vger.kernel.org, "KOSAKI Motohiro" > <kosaki.motoh...@jp.fujitsu.com>, "Paul E. McKenney" > <paul...@linux.vnet.ibm.com>, "Nicholas Miell" > <nmi...@comcast.net>, "Linus Torvalds" <torva...@linux-foundation.org>, "Ingo > Molnar" <mi...@redhat.com>, "Alan Cox" > <gno...@lxorguk.ukuu.org.uk>, "Lai Jiangshan" <la...@cn.fujitsu.com>, > "Stephen Hemminger" > <step...@networkplumber.org>, "Andrew Morton" <a...@linux-foundation.org>, > "Josh Triplett" <j...@joshtriplett.org>, > "Thomas Gleixner" <t...@linutronix.de>, "David Howells" > <dhowe...@redhat.com>, "Nick Piggin" <npig...@kernel.dk> > Sent: Monday, March 16, 2015 10:24:30 AM > Subject: Re: [RFC PATCH] sys_membarrier(): system/process-wide memory barrier > (x86) (v12) > > On Mon, 16 Mar 2015 15:19:39 +0100 > Peter Zijlstra <pet...@infradead.org> wrote: > > > > > I suppose this is an unprivileged syscall; so what do we do about: > > > > for (;;) > > sys_membar(EXPEDITED); > > > > Which would spray the entire system with IPIs at break neck speed. > > Perhaps it should be rate limited. Have parameters (controlled via > sysctl) that will only allow so many of these per ms. If it exceeds it, > then the call will end up being a schedule_timeout() till it is allowed > to continue. Thus, the above will spit out a few hundred IPIs, then > sleep for a millisecond, and then spit out another hundred IPIs and > sleep again. > > That would prevent any DoS attacks.
As I pointed out in my other email, EXPEDITED | ~PRIVATE currently returns -EINVAL. The only way to do a system-wide barrier with this membarrier implementation is to use synchronize_sched() (~EXPEDITED), which I strongly doubt would perform a DoS. If we eventually care about a EXPEDITED | ~PRIVATE implementation, then I agree that rate limiting might be a good way to do it. I would be a bit uncomfortable sending IPIs to _all_ CPUs though, even with rate limiting. But perhaps it's a non-issue ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
