Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760509AbZCaNfc (ORCPT ); Tue, 31 Mar 2009 09:35:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760482AbZCaNdd (ORCPT ); Tue, 31 Mar 2009 09:33:33 -0400 Received: from mga01.intel.com ([192.55.52.88]:25809 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760447AbZCaNda (ORCPT ); Tue, 31 Mar 2009 09:33:30 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.38,453,1233561600"; d="scan'208";a="677481212" Date: Tue, 31 Mar 2009 14:50:51 +0200 From: Markus Metzger To: linux-kernel@vger.kernel.org, mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com Cc: markus.t.metzger@intel.com, markus.t.metzger@gmail.com, roland@redhat.com, eranian@googlemail.com, oleg@redhat.com, juan.villacis@intel.com, ak@linux.jf.intel.com Subject: [patch 1/21] x86, bts: fix race when bts tracer is removed Message-ID: <20090331145051.A12111@sedona.ch.intel.com> Mime-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.2.5i Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3794 Lines: 118 When the bts tracer is removed while the traced task is running, the write to clear the bts tracer pointer races with context switch code. Read the tracer once during a context switch. When a new tracer is installed, the bts tracer is set in the ds context before the tracer is initialized in order to claim the context for that tracer. This may result in write accesses using an uninitialized trace configuration when scheduling timestamps have been requested. Store active tracing flags separately and only set active flags after the tracing configuration has been initialized. Signed-off-by: Markus Metzger --- Index: git-tip/arch/x86/kernel/ds.c =================================================================== --- git-tip.orig/arch/x86/kernel/ds.c 2009-03-30 17:47:21.000000000 +0200 +++ git-tip/arch/x86/kernel/ds.c 2009-03-30 17:48:31.000000000 +0200 @@ -89,6 +89,9 @@ struct bts_tracer { /* Buffer overflow notification function: */ bts_ovfl_callback_t ovfl; + + /* Active flags affecting trace collection. */ + unsigned int flags; }; struct pebs_tracer { @@ -799,6 +802,8 @@ void ds_suspend_bts(struct bts_tracer *t if (!tracer) return; + tracer->flags = 0; + task = tracer->ds.context->task; if (!task || (task == current)) @@ -820,6 +825,8 @@ void ds_resume_bts(struct bts_tracer *tr if (!tracer) return; + tracer->flags = tracer->trace.ds.flags; + task = tracer->ds.context->task; control = ds_cfg.ctl[dsf_bts]; @@ -1044,36 +1051,39 @@ void ds_switch_to(struct task_struct *pr { struct ds_context *prev_ctx = prev->thread.ds_ctx; struct ds_context *next_ctx = next->thread.ds_ctx; + unsigned long debugctlmsr = next->thread.debugctlmsr; if (prev_ctx) { + struct bts_tracer *tracer = prev_ctx->bts_master; + update_debugctlmsr(0); - if (prev_ctx->bts_master && - (prev_ctx->bts_master->trace.ds.flags & BTS_TIMESTAMPS)) { + if (tracer && (tracer->flags & BTS_TIMESTAMPS)) { struct bts_struct ts = { .qualifier = bts_task_departs, .variant.timestamp.jiffies = jiffies_64, .variant.timestamp.pid = prev->pid }; - bts_write(prev_ctx->bts_master, &ts); + bts_write(tracer, &ts); } } if (next_ctx) { - if (next_ctx->bts_master && - (next_ctx->bts_master->trace.ds.flags & BTS_TIMESTAMPS)) { + struct bts_tracer *tracer = next_ctx->bts_master; + + if (tracer && (tracer->flags & BTS_TIMESTAMPS)) { struct bts_struct ts = { .qualifier = bts_task_arrives, .variant.timestamp.jiffies = jiffies_64, .variant.timestamp.pid = next->pid }; - bts_write(next_ctx->bts_master, &ts); + bts_write(tracer, &ts); } wrmsrl(MSR_IA32_DS_AREA, (unsigned long)next_ctx->ds); } - update_debugctlmsr(next->thread.debugctlmsr); + update_debugctlmsr(debugctlmsr); } void ds_copy_thread(struct task_struct *tsk, struct task_struct *father) --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. -- 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/