From: Frederic Weisbecker Date: Tue, 06 Apr 2010 11:38:34 +0000 Subject: Re: Random scheduler/unaligned accesses crashes with perf lock Message-Id: <20100406113830.GF5147@nowhere> List-Id: References: <20100405065701.GC5127@nowhere> <20100405.122233.188421941.davem@davemloft.net> <20100405194055.GA5265@nowhere> <20100406.025049.267615796.davem@davemloft.net> In-Reply-To: <20100406.025049.267615796.davem@davemloft.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: David Miller Cc: sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@elte.hu, acme@redhat.com, a.p.zijlstra@chello.nl, paulus@samba.org On Tue, Apr 06, 2010 at 02:50:49AM -0700, David Miller wrote: > From: Frederic Weisbecker > Date: Mon, 5 Apr 2010 21:40:58 +0200 > > > It happens without CONFIG_FUNCTION_TRACER as well (but it happens > > when the function tracer runs). And I hadn't your > > perf_arch_save_caller_regs() when I triggered this. > > I figured out the problem, it's NMIs. As soon as I disable all of the > NMI watchdog code, the problem goes away. > > This is because some parts of the NMI interrupt handling path are not > marked with "notrace" and the various tracer code paths use > local_irq_disable() (either directly or indirectly) which doesn't work > with sparc64's NMI scheme. These essentially turn NMIs back on in the > NMI handler before the NMI condition has been cleared, and thus we can > re-enter with another NMI interrupt. > > We went through this for perf events, and we just made sure that > local_irq_{enable,disable}() never occurs in any of the code paths in > perf events that can be reached via the NMI interrupt handler. (the > only one we had was sched_clock() and that was easily fixed) That reminds me we have a new pair of local_irq_disable/enable in perf_event_task_output(), which path can be taken by hardware pmu events. See this patch: 8bb39f9aa068262732fe44b965d7a6eb5a5a7d67 perf: Fix 'perf sched record' deadlock