Re: [Patch] jbd commit code deadloop when installing Linux

Zou Nan hai
2006-06-28T07:32:15Z

On Wed, 2006-06-28 at 14:55, Andrew Morton wrote:
> On Wed, 28 Jun 2006 08:38:59 +0200
> Ingo Molnar <mingo@elte.hu> wrote:
>
> >
> > * Andrew Morton <akpm@osdl.org> wrote:
> >
> > > > We see system hang in ext3 jbd code
> > > > when Linux install program anaconda copying
> > > > packages.
> > > >
> > > > That is because anaconda is invoked from linuxrc
> > > > in initrd when system_state is still SYSTEM_BOOTING.
> >
> > [ argh ...! ]
>
> That's what I thought ;)
>
> > > > Thus the cond_resched checks in journal_commit_transaction
> > > > will always return 1 without actually schedule,
> > > > then the system fall into deadloop.
> > >
> > > That's a bug in cond_resched().
> > >
> > > Something like this..
> >
> > Acked-by: Ingo Molnar <mingo@elte.hu>
> >
>
> Thanks. Zou, it'd be great if you could test this in your setup, please.
> I've tagged it as 2.6.17.x material.

Andrew,
I am building the env to test.
The patch was my original idea, but I was afraid of breaking any code
that rely on the OLD wrong cond_sched semantic. However later I did a
grep found that there is very few code that checks the return value of
cond_resched. So the patch should be safe.

However I think cond_resched_lock and cond_resched_softirq also need fix
to make the semantic consistent.

Please check the following patch.

Zou Nan hai

Signed-off-by: Zou Nan hai <nanhai.zou@intel.com>

--- linux-2.6.17/kernel/sched.c 2006-06-18 09:49:35.000000000 +0800
+++ linux-2.6.17-fix/kernel/sched.c 2006-06-28 13:34:39.000000000 +0800
@@ -4044,7 +4044,7 @@ asmlinkage long sys_sched_yield(void)
return 0;
}

-static inline void __cond_resched(void)
+static inline int __cond_resched(void)
{
/*
* The BKS might be reacquired before we have dropped
@@ -4052,22 +4052,21 @@ static inline void __cond_resched(void)
* cond_resched() call.
*/
if (unlikely(preempt_count()))
- return;
+ return 0;
if (unlikely(system_state != SYSTEM_RUNNING))
- return;
+ return 0;
do {
add_preempt_count(PREEMPT_ACTIVE);
schedule();
sub_preempt_count(PREEMPT_ACTIVE);
} while (need_resched());
+ return 1;
}

int __sched cond_resched(void)
{
- if (need_resched()) {
- __cond_resched();
- return 1;
- }
+ if (need_resched())
+ return __cond_resched();
return 0;
}

@@ -4094,8 +4093,7 @@ int cond_resched_lock(spinlock_t *lock)
if (need_resched()) {
_raw_spin_unlock(lock);
preempt_enable_no_resched();
- __cond_resched();
- ret = 1;
+ ret |= __cond_resched();
spin_lock(lock);
}
return ret;
@@ -4106,14 +4104,13 @@ EXPORT_SYMBOL(cond_resched_lock);
int __sched cond_resched_softirq(void)
{
BUG_ON(!in_softirq());
-
+ int ret = 0;
if (need_resched()) {
__local_bh_enable();
- __cond_resched();
+ ret = __cond_resched();
local_bh_disable();
- return 1;
}
- return 0;
+ return ret;
}

EXPORT_SYMBOL(cond_resched_softirq);