Messages in this thread | | | Date | Wed, 28 Nov 2007 19:30:34 +0300 | From | Oleg Nesterov <> | Subject | Re: /proc dcache deadlock in do_exit |
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On 11/27, Eric W. Biederman wrote: > > Andrew Morton <akpm@linux-foundation.org> writes: > > > On Tue, 27 Nov 2007 14:20:22 +0100 > > Andrea Arcangeli <andrea@suse.de> wrote: > > > >> do_exit->release_task->mark_inode_dirty_sync->schedule() (will never > >> come back to run journal_stop) > > > > I don't see why the schedule() will not return? Because the task has > > PF_EXITING set? Doesn't TASK_DEAD do that? > > Yes, why do we not come back from schedule? > > If we are not allowed to schedule after setting PF_EXITING before > we set TASK_DEAD that entire code path sounds brittle and > error prone.
Yes, it is fine to schedule after release_task(). As Eric pointed out, we don't race with call_rcu(delayed_put_task_struct), scheduler has another reference
dup_task_struct: /* One for us, one for whoever does the "release_task()" (usually parent) */ atomic_set(&tsk->usage,2);
However, with CONFIG_HOTPLUG_CPU we do have the problem here, but this is off-topic. Preemption is fine, but deactivate_task() is not. We can't migrate the deactivated released task from the dead CPU.
migrate_live_tasks() can't find the task after __unhash_process()
migrate_dead_tasks() doesn't see it after deactivate_task().
And afaics try_to_wake_up() doesn't necessary change task_cpu() if it is offline.
No? But again, this is offtopic even if I am right.
Oleg.
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