Messages in this thread Patch in this message |  | | Date | Sat, 29 Sep 2001 22:50:09 -0700 | From | "Martin J. Bligh" <> | Subject | [patch] Race between init_idle and reschedule_idle |
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On an SMP system, if the boot cpu calls reschedule_idle before the secondary cpus have all called init_idle, we hit the following code in reschedule_idle:
... for (i = 0; i < smp_num_cpus; i++) { cpu = cpu_logical_map(i); if (!can_schedule(p, cpu)) continue; tsk = cpu_curr(cpu); ...
Because init_idle hasn't run for all cpus yet, the expression "cpu_curr(cpu)" gives us NULL. When we derefernce an offset of 0x50 off tsk a few nanoseconds later we panic, complaining vaddr 0x00000050 is invalid.
This is more likely to happen on larger systems, but could happen on any SMP system (especially if I enable serial console, which really slows down the secondary procs doing printk ;-) ). If you want to see the panic / analysis, I can send it.
Thanks to Alan Cox & Andrew Morton for showing me how to serialise the cpus to make the panic legible. The following patch holds back the boot cpu at the end of smp_init until all the secondarys have done init_idle:
--- virgin-2.4.10/kernel/sched.c Mon Sep 17 23:03:09 2001 +++ linux-2.4.10/kernel/sched.c Sat Sep 29 19:57:10 2001 @@ -1309,6 +1309,8 @@ atomic_inc(¤t->files->count); }
+extern volatile unsigned long wait_init_idle; + void __init init_idle(void) { struct schedule_data * sched_data; @@ -1321,6 +1323,7 @@ } sched_data->curr = current; sched_data->last_schedule = get_cycles(); + clear_bit(current->processor, &wait_init_idle); }
extern void init_timervecs (void); --- virgin-2.4.10/init/main.c Thu Sep 20 21:02:01 2001 +++ linux-2.4.10/init/main.c Sat Sep 29 21:11:52 2001 @@ -477,6 +477,8 @@ extern void setup_arch(char **); extern void cpu_idle(void);
+volatile unsigned long wait_init_idle = 0UL; + #ifndef CONFIG_SMP
#ifdef CONFIG_X86_IO_APIC @@ -490,13 +492,25 @@
#else
+ /* Called by boot processor to activate the rest. */ static void __init smp_init(void) { /* Get other processors into their bootup holding patterns. */ smp_boot_cpus(); + wait_init_idle = cpu_online_map; + clear_bit(current->processor, &wait_init_idle); /* Don't wait on me! */ + printk("Waiting on wait_init_idle (map = 0x%lx)\n", wait_init_idle); smp_threads_ready=1; smp_commence(); + + /* Wait for the other cpus to set up their idle processes */ + while (1) { + if (!wait_init_idle) + break; + rep_nop(); + } + printk("All processors have done init_idle\n"); }
#endif
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