From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Date: Wed, 19 Mar 2008 23:23:59 +0000 Subject: RE: [2.6.25-rc5-mm1][regression] ia64: hackbench doesn't finish Message-Id: <1205969039.6437.44.camel@lappy> List-Id: References: <20080318084314.FF0F.KOSAKI.MOTOHIRO@jp.fujitsu.com> <20080318094527.FF12.KOSAKI.MOTOHIRO@jp.fujitsu.com> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Yu, Fenghua" Cc: KOSAKI Motohiro , "Luck, Tony" , LKML , linux-ia64@vger.kernel.org, Hidetoshi Seto , Andrew Morton On Tue, 2008-03-18 at 17:14 -0700, Yu, Fenghua wrote: > >this paramter mean use all physical memory and about 1GB swap space. > >Could you expand swap space? > > We can reproduce the soft lockup issue now and root cause the issue as > well. > > Since the ptc.g patch uses semaphore ptcg_sem to serialize multiple > ptc.g instructions in ia64_global_tlb_purge(). This requires the code > path should be safe to sleep in down(). But the code path can not sleep > during swap because it holds some spin locks (e.g. anon_vma_lock). Going > to sleep finally causes soft lockup. > > Actually we though of this issue before releasing the ptcg patch and > wrote some non-sleeping versions of ptcg patches. But since we couldn't > see the sleeping issue during our testing, we didn't release a > non-sleeping ptcg patch. If replacing the ptcg patch in -mm1 tree with > one of our non-sleeping ptcg patches, the issue goes away. > > Tony and I are working on releasing a final ptcg patch to solve the > issue. Which makes me wonder, why did you ever use a semaphore here? Looking at the code its a straight forward mutex. And when you would have used a mutex lockdep would have warned about this. There is hardly ever a good reason to use semaphores in new code, we're trying very hard to get rid of them. Hmm, then again, does ia64 have lockdep?