From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751081AbVHKPVS (ORCPT ); Thu, 11 Aug 2005 11:21:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751084AbVHKPVS (ORCPT ); Thu, 11 Aug 2005 11:21:18 -0400 Received: from e32.co.us.ibm.com ([32.97.110.130]:62201 "EHLO e32.co.us.ibm.com") by vger.kernel.org with ESMTP id S1751081AbVHKPVR (ORCPT ); Thu, 11 Aug 2005 11:21:17 -0400 Subject: 2.6.13-rc4-mm1: Divide by zero in find_idlest_group From: Dave Kleikamp To: Con Kolivas Cc: linux-kernel Content-Type: text/plain Date: Thu, 11 Aug 2005 10:21:14 -0500 Message-Id: <1123773675.9252.11.camel@kleikamp.austin.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org I encounted this trap on a 2-way i386 box running 2.6.13-rc4-mm1: [70347.743727] divide error: 0000 [#2] [70347.752979] PREEMPT SMP DEBUG_PAGEALLOC [70347.773060] last sysfs file: /devices/pnp0/00:11/id Program received signal SIGTRAP, Trace/breakpoint trap. 0xc0119556 in find_idlest_group (sd=0xc1084dc0, p=0xc3b96030, this_cpu=0) at sched.c:1033 1033 target_load = target_load * rq->prio_bias / rq->nr_running; (gdb) where #0 0xc0119556 in find_idlest_group (sd=0xc1084dc0, p=0xc3b96030, this_cpu=0) at sched.c:1033 #1 0xc0119744 in sched_balance_self (cpu=0, flag=4) at sched.c:1151 #2 0xc011a63f in sched_exec () at sched.c:1840 #3 0xc016cacb in do_execve (filename=0xc3e35000 "/bin/sh", argv=0xbfff512c, envp=0xbfff6010, regs=0xa00) at exec.c:1162 #4 0xc0101b5a in sys_execve (regs= {ebx = -1208173323, ecx = -1073786580, edx = -1073782768, esi = -1073782768, edi = -1208107392, ebp = -1073786620, eax = 11, xds = 123, xes = -1072693125, orig_eax = 11, eip = -1208664822, xcs = 115, eflags = 658, esp = -1073786628, xss = 123}) at process.c:787 #5 0xc0102fdd in syscall_call () at current.h:9 #6 0xb7fcbcf5 in ?? () print *(struct runqueue *)0xc108c400 $1 = {lock = {raw_lock = {slock = 1}, break_lock = 0}, nr_running = 0, prio_bias = 0, cpu_load = {0, 0, 0}, nr_switches = 8877527, nr_uninterruptible = 132930, expired_timestamp = 0, timestamp_last_tick = 70347783539837, curr = 0xc1103550, idle = 0xc1103550, prev_mm = 0x0, active = 0xc108c8c0, expired = 0xc108c448, arrays = {{ nr_active = 0, bitmap = {0, 0, 0, 0, 4096}, queue = {{next = 0xc108c460, prev = 0xc108c460}, {next = 0xc108c468, prev = 0xc108c468}, { next = 0xc108c470, prev = 0xc108c470}, {next = 0xc108c478, prev = 0xc108c478}, {next = 0xc108c480, prev = 0xc108c480}, { next = 0xc108c488, prev = 0xc108c488}, {next = 0xc108c490, in __source_load, it looks like rq_nr_running must have changed between the if statement and the divide: if (rq->nr_running > 1 || (idle == NOT_IDLE && rq->nr_running)) /* * If we are busy rebalancing the load is biased by * priority to create 'nice' support across cpus. When * idle rebalancing we should only bias the source_load if * there is more than one task running on that queue to * prevent idle rebalance from trying to pull tasks from a * queue with only one running task. */ source_load = source_load * rq->prio_bias / rq->nr_running; Should there be any locking around this? Or should the value of rq->nr_running be saved to a local variable as in this untested patch? diff -urp linux-2.6.13-rc5-mm1/kernel/sched.c linux/kernel/sched.c --- linux-2.6.13-rc5-mm1/kernel/sched.c 2005-08-11 09:41:30.000000000 -0500 +++ linux/kernel/sched.c 2005-08-11 09:47:27.000000000 -0500 @@ -989,15 +989,16 @@ void kick_process(task_t *p) static inline unsigned long __source_load(int cpu, int type, enum idle_type idle) { runqueue_t *rq = cpu_rq(cpu); + unsigned long running = rq->nr_running; unsigned long source_load, cpu_load = rq->cpu_load[type-1], - load_now = rq->nr_running * SCHED_LOAD_SCALE; + load_now = running * SCHED_LOAD_SCALE; if (type == 0) source_load = load_now; else source_load = min(cpu_load, load_now); - if (rq->nr_running > 1 || (idle == NOT_IDLE && rq->nr_running)) + if (running > 1 || (idle == NOT_IDLE && running)) /* * If we are busy rebalancing the load is biased by * priority to create 'nice' support across cpus. When @@ -1006,7 +1007,7 @@ static inline unsigned long __source_loa * prevent idle rebalance from trying to pull tasks from a * queue with only one running task. */ - source_load = source_load * rq->prio_bias / rq->nr_running; + source_load = source_load * rq->prio_bias / running; return source_load; } @@ -1022,16 +1023,17 @@ static inline unsigned long source_load( static inline unsigned long __target_load(int cpu, int type, enum idle_type idle) { runqueue_t *rq = cpu_rq(cpu); + unsigned long running = rq->nr_running; unsigned long target_load, cpu_load = rq->cpu_load[type-1], - load_now = rq->nr_running * SCHED_LOAD_SCALE; + load_now = running * SCHED_LOAD_SCALE; if (type == 0) target_load = load_now; else target_load = max(cpu_load, load_now); - if (rq->nr_running > 1 || (idle == NOT_IDLE && rq->nr_running)) - target_load = target_load * rq->prio_bias / rq->nr_running; + if (running > 1 || (idle == NOT_IDLE && running)) + target_load = target_load * rq->prio_bias / running; return target_load; } -- David Kleikamp IBM Linux Technology Center