Re: [Patch] restore the RCU callback to defer put_task_struct() Re: Problems with 2.6.17-rt8

Bill Huey
2006-08-18T12:00:09Z

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On Tue, Aug 15, 2006 at 10:53:10AM -0700, Robert Crocombe wrote:
> NUMA emulation is off in the most recent one (the most recent config
> posted), and the high Hz is due to 'man nanosleep':
>
> BUGS
> The current implementation of nanosleep() is based on the normal
> kernel
> timer mechanism, which has a resolution of 1/HZ s (see
> time(7)).
> Therefore, nanosleep() pauses always for at least the specified
> time,
> however it can take up to 10 ms longer than specified until the
> process
> becomes runnable again. For the same reason, the value returned in
> case
> of a delivered signal in *rem is usually rounded to the next
> larger
> multiple of 1/HZ s.
>
> and Other People's Code (tm).
>
> Sadly, I am behind a firewall and cannot offer remote access to the
> machine. If you can point out some other config options that are Not
> Good, then I can see about pruning them.

Robert,

Sorry for the delay, been a bit distracted.

There's a lot of little problems in the stacks traces you sent and I wonder
how much it effects the rest of the system. Getting reliable debug output
has been a bit problematic.

Can you try this patch and see if it changes something ?

1) This fixes a flush_tlb_mm atomic violation by moving back to a spinlock

2) Moves the delay logic up higher in the tree from free_task() to __put_task_struct()

3) Adds a check to all calls to rt_lock() where it will panic() the kernel
so that I can get a decent stack trace.

4) Minor fixes to the original deference code for INIT_TASK

5) use stop_trace just before doing any real panic().

This may not fix the journald code, but it should at least eliminate a
couple of stack traces that might be creating other effects in the system
and stop it dead in it's tracks. Hope this is useful.

Patch attached:

bill

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#
============================================================
--- arch/x86_64/kernel/smp.c b354a6e4a080ad49f4213ab4334ca2e57ddf1bdc
+++ arch/x86_64/kernel/smp.c a76a90aaad275ab3775d32ac3ae500fe120c5b8c
@@ -57,7 +57,7 @@
struct mm_struct *flush_mm;
unsigned long flush_va;
#define FLUSH_ALL -1ULL
- spinlock_t tlbstate_lock;
+ raw_spinlock_t tlbstate_lock;
};
char pad[SMP_CACHE_BYTES];
} ____cacheline_aligned;
============================================================
--- arch/x86_64/mm/numa.c 72976a7a4aff795f020f34e91e98e0defa280d3b
+++ arch/x86_64/mm/numa.c 4c2bb1ecc151dd04dbe28b6a4825f813efcab17d
@@ -12,6 +12,8 @@
#include <linux/module.h>
#include <linux/nodemask.h>

+#include <linux/dobject.h>
+
#include <asm/e820.h>
#include <asm/proto.h>
#include <asm/dma.h>
@@ -317,6 +319,7 @@
{
int i;
unsigned long pages = 0;
+
for_each_online_node(i) {
pages += free_all_bootmem_node(NODE_DATA(i));
}
============================================================
--- include/linux/init_task.h 938a1587ab9e35bb8d24cf843d4e7424e3030a4c
+++ include/linux/init_task.h b7acecacd94e4ee753c833bc8dd84623975927f9
@@ -126,7 +126,8 @@
.cpu_timers = INIT_CPU_TIMERS(tsk.cpu_timers), \
.fs_excl = ATOMIC_INIT(0), \
.posix_timer_list = NULL, \
- INIT_RT_MUTEXES(tsk) \
+ INIT_RT_MUTEXES(tsk), \
+ .delayed_drop = LIST_HEAD_INIT(tsk.delayed_drop) \
}

============================================================
--- include/linux/sched.h 0ed8993484be9c13728f4ebdaa51fc0f0c229018
+++ include/linux/sched.h c65ebaa452498f611280baafd8ee6282ea0746f2
@@ -1082,6 +1091,9 @@
* cache last used pipe for splice
*/
struct pipe_inode_info *splice_pipe;
+
+ /* --billh */
+ struct list_head delayed_drop; // should investigate how do_fork() handles this as well
};

static inline pid_t process_group(struct task_struct *tsk)
============================================================
--- include/linux/seqlock.h e0e6ee774c4c5dd9f3e0fd4d3ada566cda45d11b
+++ include/linux/seqlock.h d0b08ef3758e5c0fa679d44a67582ca0b03878de
@@ -1,8 +1,8 @@
#ifndef __LINUX_SEQLOCK_H
#define __LINUX_SEQLOCK_H
/*
* Reader/writer consistent mechanism without starving writers. This type of
- * lock for data where the reader wants a consitent set of information
+ * lock for data where the reader wants a consistent set of information
* and is willing to retry if the information changes. Readers never
* block but they may have to retry if a writer is in
* progress. Writers do not wait for readers.
============================================================
--- init/main.c b9d35fb2830863866491a774c71f2516c02afe54
+++ init/main.c 8b432cd1d2f9b3f318a0b43783642b93f208012c
@@ -57,6 +57,8 @@
#include <asm/sections.h>
#include <asm/cacheflush.h>

+#include <linux/dobject.h>
+
#ifdef CONFIG_X86_LOCAL_APIC
#include <asm/smp.h>
#endif
============================================================
--- kernel/exit.c f4cc2f8e48a262bd26b6fc5d1253a8482c8c2d04
+++ kernel/exit.c 38720025341ef0a1c923a06ecf330fffb718c62c
@@ -131,11 +131,6 @@
}
}

-static void delayed_put_task_struct(struct rcu_head *rhp)
-{
- put_task_struct(container_of(rhp, struct task_struct, rcu));
-}
-
void release_task(struct task_struct * p)
{
int zap_leader;
@@ -177,7 +172,7 @@
spin_unlock(&p->proc_lock);
proc_pid_flush(proc_dentry);
release_thread(p);
- call_rcu(&p->rcu, delayed_put_task_struct);
+ put_task_struct(p);

p = leader;
if (unlikely(zap_leader))
============================================================
--- kernel/fork.c 506dabd42d242f78e0321594c7723481e0cd87dc
+++ kernel/fork.c 100e4301ffaa9bb8afcb1dd00d02914b1f680ebe
@@ -47,6 +47,8 @@
#include <linux/notifier.h>
#include <linux/cn_proc.h>

+#include <linux/preempt.h> //--billh
+
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
#include <asm/uaccess.h>
@@ -75,7 +77,10 @@
*/
static DEFINE_PER_CPU(struct task_struct *, desched_task);

-static DEFINE_PER_CPU(struct list_head, delayed_drop_list);
+static DEFINE_PER_CPU(struct list_head, delayed_mmdrop_list);
+#ifdef CONFIG_PREEMPT_RT
+static DEFINE_PER_CPU(struct list_head, delayed_put_task_struct_list); //--bilh
+#endif

int nr_processes(void)
{
@@ -120,7 +125,17 @@
}
EXPORT_SYMBOL(free_task);

+void fastcall free_task_delayed(struct task_struct *task);
+
+/*
+ * Delay if this is in an atomic critical section otherwise inline the deallocation
+ * --billh
+ */
+#ifdef CONFIG_PREEMPT_RT
+void __put_task_struct_inline(struct task_struct *tsk)
+#else
void __put_task_struct(struct task_struct *tsk)
+#endif
{
WARN_ON(!(tsk->exit_state & (EXIT_DEAD | EXIT_ZOMBIE)));
BUG_ON(atomic_read(&tsk->usage));
@@ -134,7 +149,7 @@
if (!profile_handoff_task(tsk))
free_task(tsk);
}
-
+
void __init fork_init(unsigned long mempages)
{
int i;
@@ -167,8 +182,12 @@
init_task.signal->rlim[RLIMIT_SIGPENDING] =
init_task.signal->rlim[RLIMIT_NPROC];

- for (i = 0; i < NR_CPUS; i++)
- INIT_LIST_HEAD(&per_cpu(delayed_drop_list, i));
+ for (i = 0; i < NR_CPUS; i++) {
+ INIT_LIST_HEAD(&per_cpu(delayed_mmdrop_list, i));
+#ifdef CONFIG_PREEMPT_RT
+ INIT_LIST_HEAD(&per_cpu(delayed_put_task_struct_list, i)); //--billh
+#endif
+ }
}

static struct task_struct *dup_task_struct(struct task_struct *orig)
@@ -1067,6 +1086,9 @@
#endif

rt_mutex_init_task(p);
+#ifdef CONFIG_PREEMPT_RT
+ INIT_LIST_HEAD(&p->delayed_drop); //--billh
+#endif

#ifdef CONFIG_DEBUG_MUTEXES
p->blocked_on = NULL; /* not blocked yet */
@@ -1693,24 +1715,73 @@
return err;
}

+static void _wake_cpu_desched_task(void)
+{
+ struct task_struct *desched_task;
+
+ desched_task = __get_cpu_var(desched_task);
+ if (desched_task)
+ wake_up_process(desched_task);
+}
+
+#ifdef CONFIG_PREEMPT_RT
+static int put_task_struct_complete(void)
+{
+ struct list_head *head;
+ int ret = 0;
+
+ head = &get_cpu_var(delayed_put_task_struct_list);
+ while (!list_empty(head)) {
+ struct task_struct *task = list_entry(head->next,
+ struct task_struct, delayed_drop);
+ list_del(&task->delayed_drop);
+ put_cpu_var(delayed_put_task_struct_list);
+
+ __put_task_struct_inline(task); // call the original function to perform the operation
+ ret = 1;
+
+ head = &get_cpu_var(delayed_put_task_struct_list);
+ }
+ put_cpu_var(delayed_put_task_struct_list);
+
+ return ret;
+}
+
+/*
+ * We dont want to do complex work from the scheduler with preemption
+ * disabled, therefore we delay the work to a per-CPU worker thread.
+ */
+void fastcall __put_task_struct(struct task_struct *task)
+{
+ struct list_head *head;
+
+ head = &get_cpu_var(delayed_put_task_struct_list);
+ list_add_tail(&task->delayed_drop, head);
+
+ _wake_cpu_desched_task();
+
+ put_cpu_var(delayed_put_task_struct_list);
+}
+#endif
+
static int mmdrop_complete(void)
{
struct list_head *head;
int ret = 0;

- head = &get_cpu_var(delayed_drop_list);
+ head = &get_cpu_var(delayed_mmdrop_list);
while (!list_empty(head)) {
struct mm_struct *mm = list_entry(head->next,
struct mm_struct, delayed_drop);
list_del(&mm->delayed_drop);
- put_cpu_var(delayed_drop_list);
+ put_cpu_var(delayed_mmdrop_list);

__mmdrop(mm);
ret = 1;

- head = &get_cpu_var(delayed_drop_list);
+ head = &get_cpu_var(delayed_mmdrop_list);
}
- put_cpu_var(delayed_drop_list);
+ put_cpu_var(delayed_mmdrop_list);

return ret;
}
@@ -1721,15 +1792,14 @@
*/
void fastcall __mmdrop_delayed(struct mm_struct *mm)
{
- struct task_struct *desched_task;
struct list_head *head;

- head = &get_cpu_var(delayed_drop_list);
+ head = &get_cpu_var(delayed_mmdrop_list);
list_add_tail(&mm->delayed_drop, head);
- desched_task = __get_cpu_var(desched_task);
- if (desched_task)
- wake_up_process(desched_task);
- put_cpu_var(delayed_drop_list);
+
+ _wake_cpu_desched_task();
+
+ put_cpu_var(delayed_mmdrop_list);
}

static int desched_thread(void * __bind_cpu)
@@ -1743,6 +1813,9 @@

if (mmdrop_complete())
continue;
+ if (put_task_struct_complete())
+ continue;
+
schedule();

/* This must be called from time to time on ia64, and is a no-op on other archs.
@@ -1767,7 +1840,10 @@
case CPU_UP_PREPARE:

BUG_ON(per_cpu(desched_task, hotcpu));
- INIT_LIST_HEAD(&per_cpu(delayed_drop_list, hotcpu));
+ INIT_LIST_HEAD(&per_cpu(delayed_mmdrop_list, hotcpu));
+#ifdef CONFIG_PREEMPT_RT
+ INIT_LIST_HEAD(&per_cpu(delayed_put_task_struct_list, hotcpu)); // --billh
+#endif
p = kthread_create(desched_thread, hcpu, "desched/%d", hotcpu);
if (IS_ERR(p)) {
printk("desched_thread for %i failed\n", hotcpu);
============================================================
--- kernel/rtmutex.c d9e1288a369758ad7144999ef59019a51e17ce7a
+++ kernel/rtmutex.c 5c47b3b44b13667f0eb0424fe1653cbdfc8dac00
@@ -13,6 +13,9 @@
#include <linux/sched.h>
#include <linux/timer.h>

+#include <linux/hardirq.h> //-billh
+#include <linux/interrupt.h> //-billh
+
#include "rtmutex_common.h"

#ifdef CONFIG_DEBUG_RT_MUTEXES
@@ -740,7 +743,19 @@

void __lockfunc rt_lock(struct rt_mutex *lock)
{
+ if (
+ (system_state == SYSTEM_RUNNING) &&
+ in_atomic() &&
+ !current->exit_state &&
+ !oops_in_progress
+ ) {
+ stop_trace();
+ panic("%s: in atomic: " "%s/0x%08x/%d\n",
+ __func__, current->comm, preempt_count(), current->pid);
+ }
+
rt_lock_fastlock(lock, rt_lock_slowlock);
+
}
EXPORT_SYMBOL(rt_lock);