Messages in this thread | | | Date | Mon, 15 Jan 2007 15:54:01 +0300 | From | Oleg Nesterov <> | Subject | Re: [PATCH] flush_cpu_workqueue: don't flush an empty ->worklist |
| |
On 01/15, Srivatsa Vaddagiri wrote: > > On Mon, Jan 15, 2007 at 02:54:10AM +0300, Oleg Nesterov wrote: > > How about the pseudo-code below? > > Some quick comments: > > - singlethread_cpu needs to be hotplug safe (broken currently)
Why? Could you explain?
> - Any reason why cpu_populated_map is not modified on CPU_DEAD?
Because CPU_DEAD/CPU_UP_CANCELED doesn't wait for cwq->thread to exit. cpu_populated_map never shrinks, it only grows on CPU_UP_PREPARE.
We can change this, but it needs some more code, and I am not sure we need it. Note that a "false" bit in cpu_populated_map only means that flush_work/flush_workqueue/destroy_workqueu will do lock/unlock of cwq->lock, nothing more.
> - I feel more comfortable if workqueue_cpu_callback were to take > workqueue_mutex in LOCK_ACQ and release it in LOCK_RELEASE > notifications.
The whole purpose of this change to avoid this!
Gautham R Shenoy wrote: > > Oh! I was refering to the other set of workqueue deadlock woes. The > ones caused when subsystems (like cpufreq) try to create/destroy > workqueue from the cpuhotplug callback path. > > Creation/destruction of workqueue requires us to take workqueue_mutex, > which would have already been taken during CPU_LOCK_ACQUIRE.
With this change workqueue_mutex is only taken to protect workqueues list, why should we hold it for (say) CPU_UP_PREPARE->CPU_ONLINE path?
> This will provide stable access to cpu_populated_map > to functions like __create_workqueue.
I think this is not needed.
> Finally, I wonder if these changes will be unnecessary if we move to > process freezer based hotplug locking ...
This change ir not strictly necessary but imho make the code better and shrinks .text by 379 bytes.
But I believe that freezer will change nothing for workqueue. We still need take_over_work(), and hacks like migrate_sequence. And no, CPU_DEAD can't just thaw cwq->thread which was bound to the dead CPU to complete kthread_stop(), we should thaw all processes.
Oleg.
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |