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
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