From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753460AbZCKHSY (ORCPT ); Wed, 11 Mar 2009 03:18:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751938AbZCKHSO (ORCPT ); Wed, 11 Mar 2009 03:18:14 -0400 Received: from ey-out-2122.google.com ([74.125.78.25]:30037 "EHLO ey-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751923AbZCKHSO (ORCPT ); Wed, 11 Mar 2009 03:18:14 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=R1Pe4XtmV0k3W6Rr/jiZ7QRJtWcmBOf8On4k50s5Xcg+tKEBLzn/M9pH6kqja/0PyC Rk+/Juiaq2dNQK8wwTeHVYTq+PnWxzbzjEMVP1uZ19wOwBK6syueVBEqOu3W14nAbAPH GOeTC4Suyz+OXO7FR7TQwuJow/4BUF+iYWxj4= Date: Wed, 11 Mar 2009 08:18:09 +0100 From: Frederic Weisbecker To: Peter Zijlstra Cc: Steven Rostedt , LKML , Ingo Molnar , Andrew Morton Subject: Re: [GIT PULL] tracing: use raw spinlocks for trace_vprintk Message-ID: <20090311071808.GA5090@nowhere> References: <1236754764.22914.3680.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1236754764.22914.3680.camel@twins> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 11, 2009 at 07:59:24AM +0100, Peter Zijlstra wrote: > On Tue, 2009-03-10 at 21:26 -0400, Steven Rostedt wrote: > > > commit 80370cb758e7ca2692cd9fb5e413d970b1f4b2b2 > > Author: Steven Rostedt > > Date: Tue Mar 10 17:16:35 2009 -0400 > > > > tracing: use raw spinlocks for trace_vprintk > > > > Impact: prevent locking up by lockdep tracer > > > > The lockdep tracer uses trace_vprintk and thus trace_vprintk can not > > call back into lockdep without locking up. > > Hmm, I did this when I posted the lockdep tracepoints, so someone then > did a bad copy/paste job when renaming ftrace_printk or something? > > See efed792d6738964f399a508ef9e831cd60fa4657 Must be my bad :-s I think I lost this modification that was done on the old trace_vprintf between two iterations of the bprintk patchset. BTW, Ingo reported one or two monthes ago that ftrace_printk was not NMI safe because of this spinlock. He suggested to drop the spinlock and then make trace_buf per_cpu. By disabling the irq we prevent from race with maskable irqs. And in case of racy accesses to trace_buf because of an nmi, then the buffer might be mixed up but it must be harmless compared to a hardlockup that can occur now. On the worst case, the trace will be weird and that's it. Frederic. > > Signed-off-by: Steven Rostedt > > > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > > index 8c6a902..4c97947 100644 > > --- a/kernel/trace/trace.c > > +++ b/kernel/trace/trace.c > > @@ -1176,7 +1176,8 @@ void trace_graph_return(struct ftrace_graph_ret *trace) > > */ > > int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args) > > { > > - static DEFINE_SPINLOCK(trace_buf_lock); > > + static raw_spinlock_t trace_buf_lock = > > + (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED; > > static u32 trace_buf[TRACE_BUF_SIZE]; > > > > struct ring_buffer_event *event; > > @@ -1201,7 +1202,9 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args) > > if (unlikely(atomic_read(&data->disabled))) > > goto out; > > > > - spin_lock_irqsave(&trace_buf_lock, flags); > > + /* Lockdep uses trace_printk for lock tracing */ > > + local_irq_save(flags); > > Shouldn't you also use raw_local_irq_save() and friends? > > > + __raw_spin_lock(&trace_buf_lock); > > len = vbin_printf(trace_buf, TRACE_BUF_SIZE, fmt, args); > > > > if (len > TRACE_BUF_SIZE || len < 0) > > @@ -1220,7 +1223,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args) > > ring_buffer_unlock_commit(tr->buffer, event); > > > > out_unlock: > > - spin_unlock_irqrestore(&trace_buf_lock, flags); > > + __raw_spin_unlock(&trace_buf_lock); > > + local_irq_restore(flags); > > > > out: > > ftrace_preempt_enable(resched); > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/