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Subject[PATCH 0/1] hung_task: fix the broken rcu_lock_break() logic
On 02/17, Oleg Nesterov wrote:
> On 02/17, Tetsuo Handa wrote:
> >
> > Oleg Nesterov wrote:
> > > int main(void)
> > > {
> > > vfork();
> > > pause();
> > > }
> >^
> > Wow!
> and this reminds me... check_hung_uninterruptible_tasks() is very broken,
> it can crash the kernel itself. I'll resend my ancient fixes once again
> today, maybe this resend will be successful ;)

Please apply.

The patch was sent more than a year ago, I preserved the acks I got.

I was also going to add the PF_FREEZER_SKIP check in check_hung_task(),
but this was already done: f9fab10bbd768b0e5254e53a4a8477a94bfc4b96.
This means I lied, the program above no longer creates the problem
for check_hung_uninterruptible_tasks(). But that was not the point
for make-it-killable anyway.

I simply can't understand why do we have sysctl_hung_task_check_count,
may be someone can explain... OK, we need to do rcu_read_unlock()
from time to time even if need_resched() is not set, that is why
we have HUNG_TASK_BATCHING. Although perhaps it makes sense to do

- if (!--batch_count)
+ if (!--batch_count || need_resched())

but max_count? I guess I missed something obvious.


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