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SubjectRe: [PATCH 2/2] Futex non-page-pinning fix
Dave Hansen <haveblue@us.ibm.com> wrote:
>
> On Tue, 2003-09-02 at 18:16, Andrew Morton wrote:
> > Rusty Russell <rusty@rustcorp.com.au> wrote:
> > >
> > > I don't know of a rule which says "thou shalt not wake a random thread
> > > in the kernel": for all I know wierd things like CPU hotplug or
> > > software suspend may do this in the future.
> >
> > pdflush is sensitive to that. It emits angry squeaks if unexpectedly woken.
> >
> > And up until a couple of months ago there were sporadic squeaking reports,
> > but they seem to have gone away.
>
> I still run into the pdflush problem once a month or so, but only with
> boxes that are up for a week or more. It usually takes the box down if
> for no other reason than it's too busy prink()ing to do anything else.

That serves you right for not telling me!

> I haven't been able to sysrq it and the particular box that it happens
> on doesn't like NMIs so kgdb and the NMI oopser are out.
>
> Are there any good reasons not to do something like the attached patch?
> It would at least keep pdflush from evicting everthing interesting that
> may have preceded it in dmesg.

I'd prefer a more intricate patch which does something like the below.

Seriously, please: this shouldn't be happening. We need to work out the
cause.



mm/pdflush.c | 18 +++++++++++++++++-
1 files changed, 17 insertions(+), 1 deletion(-)
diff -puN mm/pdflush.c~pdflush-diag mm/pdflush.c
--- 25/mm/pdflush.c~pdflush-diag 2003-09-02 19:50:13.000000000 -0700
+++ 25-akpm/mm/pdflush.c 2003-09-02 19:53:38.000000000 -0700
@@ -84,6 +84,8 @@ struct pdflush_work {
unsigned long when_i_went_to_sleep;
};

+static int wakeup_count = 100;
+
static int __pdflush(struct pdflush_work *my_work)
{
daemonize("pdflush");
@@ -112,7 +114,10 @@ static int __pdflush(struct pdflush_work

spin_lock_irq(&pdflush_lock);
if (!list_empty(&my_work->list)) {
- printk("pdflush: bogus wakeup!\n");
+ if (wakeup_count > 0) {
+ wakeup_count--;
+ printk("pdflush: bogus wakeup!\n");
+ }
my_work->fn = NULL;
continue;
}
@@ -182,6 +187,7 @@ int pdflush_operation(void (*fn)(unsigne
{
unsigned long flags;
int ret = 0;
+ static int poke_count = 0;

if (fn == NULL)
BUG(); /* Hard to diagnose if it's deferred */
@@ -190,9 +196,19 @@ int pdflush_operation(void (*fn)(unsigne
if (list_empty(&pdflush_list)) {
spin_unlock_irqrestore(&pdflush_lock, flags);
ret = -1;
+ if (wakeup_count < 100 && poke_count < 10) {
+ printk("%s: no threads\n", __FUNCTION__);
+ dump_stack();
+ poke_count++;
+ }
} else {
struct pdflush_work *pdf;

+ if (wakeup_count < 100 && poke_count < 10) {
+ printk("%s: found a thread\n", __FUNCTION__);
+ dump_stack();
+ poke_count++;
+ }
pdf = list_entry(pdflush_list.next, struct pdflush_work, list);
list_del_init(&pdf->list);
if (list_empty(&pdflush_list))
_

-
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