From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from song.cn.fujitsu.com (unknown [222.73.24.84]) by ozlabs.org (Postfix) with ESMTP id 09A49B70A9 for ; Fri, 22 Oct 2010 18:21:45 +1100 (EST) Message-ID: <4CC13BB8.7090003@cn.fujitsu.com> Date: Fri, 22 Oct 2010 15:22:32 +0800 From: Li Zefan MIME-Version: 1.0 To: Anton Blanchard , subrata@linux.vnet.ibm.com Subject: Re: [PATCH] powerpc: Fix hcall tracepoint recursion 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> In-Reply-To: <20101021215212.4a982c85@kryten> Content-Type: text/plain; charset=ISO-8859-1 Cc: ltp-list@lists.sourceforge.net, Peter Zijlstra , LKML , Steven Rostedt , Paul Mackerras , Ingo Molnar , linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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? > 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 > >