From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755171Ab0JVHZy (ORCPT ); Fri, 22 Oct 2010 03:25:54 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:42921 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753104Ab0JVHZx (ORCPT ); Fri, 22 Oct 2010 03:25:53 -0400 Subject: Re: [PATCH] powerpc: Fix hcall tracepoint recursion From: Subrata Modak Reply-To: subrata@linux.vnet.ibm.com To: Li Zefan Cc: Anton Blanchard , ltp-list@lists.sourceforge.net, Steven Rostedt , Ingo Molnar , Peter Zijlstra , Paul Mackerras , LKML , linuxppc-dev@lists.ozlabs.org In-Reply-To: <4CC13BB8.7090003@cn.fujitsu.com> References: <4C85A88D.10700@cn.fujitsu.com> <1285689961.11429.12.camel@subratamodak.linux.ibm.com> <1286954486.4893.15.camel@subratamodak.linux.ibm.com> <4CB55FE6.6000604@cn.fujitsu.com> <4CB5615C.4070406@cn.fujitsu.com> <4CB59825.7060504@cn.fujitsu.com> <1286995066.4893.17.camel@subratamodak.linux.ibm.com> <4CBBBCB0.8070406@cn.fujitsu.com> <20101021215212.4a982c85@kryten> <4CC13BB8.7090003@cn.fujitsu.com> Content-Type: text/plain Organization: IBM Date: Fri, 22 Oct 2010 12:55:50 +0530 Message-Id: <1287732351.4949.0.camel@subratamodak.linux.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.12.3 (2.12.3-8.el5_2.2) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2010-10-22 at 15:22 +0800, Li Zefan wrote: > Anton Blanchard wrote: > > Hi, > > > >> This is a dead loop: > >> > >> trace_hcall_entry() -> trace_clock_global() -> trace_hcall_entry() .. > >> > >> And this is a PPC specific bug. Hope some ppc guys will fix it? > >> Or we kill trace_clock_global() if no one actually uses it.. > > > > Nasty! How does the patch below look? I had to disable irqs otherwise > > we would sometimes drop valid events (if we take an interrupt anywhere > > in the region where depth is elevated, then the entire interrupt will > > be blocked from calling hcall tracepoints. > > > > Thanks! > > Subrata, could you test the patch below? Yes, definitely. Givmme some time. Regards-- Subrata > > > Anton > > -- > > > > Subject: [PATCH] powerpc: Fix hcall tracepoint recursion > > > > Spinlocks on shared processor partitions use H_YIELD to notify the > > hypervisor we are waiting on another virtual CPU. Unfortunately this means > > the hcall tracepoints can recurse. > > > > The patch below adds a percpu depth and checks it on both the entry and > > exit hcall tracepoints. > > > > Signed-off-by: Anton Blanchard > > --- > > > > Index: powerpc.git/arch/powerpc/platforms/pseries/lpar.c > > =================================================================== > > --- powerpc.git.orig/arch/powerpc/platforms/pseries/lpar.c 2010-10-21 17:32:00.980003644 +1100 > > +++ powerpc.git/arch/powerpc/platforms/pseries/lpar.c 2010-10-21 17:34:54.942681273 +1100 > > @@ -701,6 +701,13 @@ EXPORT_SYMBOL(arch_free_page); > > /* NB: reg/unreg are called while guarded with the tracepoints_mutex */ > > extern long hcall_tracepoint_refcount; > > > > +/* > > + * Since the tracing code might execute hcalls we need to guard against > > + * recursion. One example of this are spinlocks calling H_YIELD on > > + * shared processor partitions. > > + */ > > +static DEFINE_PER_CPU(unsigned int, hcall_trace_depth); > > + > > void hcall_tracepoint_regfunc(void) > > { > > hcall_tracepoint_refcount++; > > @@ -713,12 +720,42 @@ void hcall_tracepoint_unregfunc(void) > > > > void __trace_hcall_entry(unsigned long opcode, unsigned long *args) > > { > > + unsigned long flags; > > + unsigned int *depth; > > + > > + local_irq_save(flags); > > + > > + depth = &__get_cpu_var(hcall_trace_depth); > > + > > + if (*depth) > > + goto out; > > + > > + (*depth)++; > > trace_hcall_entry(opcode, args); > > + (*depth)--; > > + > > +out: > > + local_irq_restore(flags); > > } > > > > void __trace_hcall_exit(long opcode, unsigned long retval, > > unsigned long *retbuf) > > { > > + unsigned long flags; > > + unsigned int *depth; > > + > > + local_irq_save(flags); > > + > > + depth = &__get_cpu_var(hcall_trace_depth); > > + > > + if (*depth) > > + goto out; > > + > > + (*depth)++; > > trace_hcall_exit(opcode, retval, retbuf); > > + (*depth)--; > > + > > +out: > > + local_irq_restore(flags); > > } > > #endif > > > >