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    SubjectRe: [PATCH] sched: add a stacktrace on enqueue_pushable error
    Hi,

    I could reproduce the bug on an intel architecture.
    I found where the problem is.
    I'll post the patch in a few hours.

    Gilles.

    Gregory Haskins wrote:
    > Hi Chirag,
    > Please apply this patch to your 26.5-rt9 tree for ppc64, enable
    > CONFIG_PROVE_LOCKING (which enables CONFIG_STACKTRACE) and give it a whirl.
    > If you get an oops, please post the console output.
    >
    > Thanks!
    >
    > -Greg
    >
    > ------------------
    > sched: add a stacktrace on enqueue_pushable error
    >
    > NOT FOR INCLUSION!
    >
    > This is to help debug an issue discovered by Chirag Jog in the thread
    >
    > http://lkml.org/lkml/2008/9/25/189
    >
    > Signed-off-by: Gregory Haskins <ghaskins@novell.com>
    > ---
    >
    > include/linux/sched.h | 6 ++++++
    > kernel/sched_rt.c | 20 +++++++++++++++++++-
    > 2 files changed, 25 insertions(+), 1 deletions(-)
    >
    > diff --git a/include/linux/sched.h b/include/linux/sched.h
    > index 67da014..53e8a6a 100644
    > --- a/include/linux/sched.h
    > +++ b/include/linux/sched.h
    > @@ -87,6 +87,7 @@ struct sched_param {
    > #include <linux/task_io_accounting.h>
    > #include <linux/kobject.h>
    > #include <linux/latencytop.h>
    > +#include <linux/stacktrace.h>
    >
    > #include <asm/processor.h>
    >
    > @@ -1170,6 +1171,11 @@ struct task_struct {
    >
    > struct list_head tasks;
    > struct plist_node pushable_tasks;
    > + struct {
    > + unsigned long data[15];
    > + struct stack_trace trace;
    > + pid_t pid;
    > + } pushable_stack;
    >
    > /*
    > * ptrace_list/ptrace_children forms the list of my children
    > diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
    > index 57a0c0d..0e6a88c 100644
    > --- a/kernel/sched_rt.c
    > +++ b/kernel/sched_rt.c
    > @@ -55,7 +55,25 @@ static void update_rt_migration(struct rq *rq)
    >
    > static void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
    > {
    > - plist_del(&p->pushable_tasks, &rq->rt.pushable_tasks);
    > + if (plist_node_empty(&p->pushable_tasks)) {
    > + struct stack_trace *trace = &p->pushable_stack.trace;
    > +
    > + trace->nr_entries = 0;
    > + trace->max_entries = sizeof(p->pushable_stack.data)/sizeof(p->pushable_stack.data[0]);
    > + trace->entries = &p->pushable_stack.data[0];
    > + trace->skip = 0;
    > +
    > + save_stack_trace(trace);
    > +
    > + p->pushable_stack.pid = current->pid;
    > + } else {
    > + printk(KERN_CRIT "redundant enqueue by %d detected\n",
    > + p->pushable_stack.pid);
    > + print_stack_trace(&p->pushable_stack.trace, 5);
    > +
    > + BUG_ON(!plist_node_empty(&p->pushable_tasks));
    > + }
    > +
    > plist_node_init(&p->pushable_tasks, p->prio);
    > plist_add(&p->pushable_tasks, &rq->rt.pushable_tasks);
    > }
    >
    > --
    > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
    > the body of a message to majordomo@vger.kernel.org
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    >
    >

    --
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Gilles.Carry
    Linux Project team
    mailto: gilles.carry@bull.net
    Phone: +33 (0)4 76 29 74 27
    Addr.: BULL S.A. 1 rue de Provence, B.P. 208 38432 Echirolles Cedex
    http://www.bull.com
    http://www.bullopensource.org/
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


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