Hi Eric,
On Tue, Jun 2, 2009 at 9:51 AM, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
> Pekka Enberg <penberg@xxxxxxxxxxxxxx> writes:
>
>> Hi Eric,
>>
>> On Tue, Jun 2, 2009 at 12:50 AM, Eric W. Biederman
>> <ebiederm@xxxxxxxxxxxx> wrote:
>>> +#ifdef CONFIG_FILE_HOTPLUG
>>> +
>>> +static bool file_in_use(struct file *file)
>>> +{
>>> + struct task_struct *leader, *task;
>>> + bool in_use = false;
>>> + int i;
>>> +
>>> + rcu_read_lock();
>>> + do_each_thread(leader, task) {
>>> + for (i = 0; i < MAX_FILE_HOTPLUG_LOCK_DEPTH; i++) {
>>> + if (task->file_hotplug_lock[i] == file) {
>>> + in_use = true;
>>> + goto found;
>>> + }
>>> + }
>>> + } while_each_thread(leader, task);
>>> +found:
>>> + rcu_read_unlock();
>>> + return in_use;
>>> +}
>>
>> This seems rather heavy-weight. If we're going to use this
>> infrastructure for forced unmount, I think this will be a problem.
>
>> Can't we two this in two stages: (1) mark a bit that forces
>> file_hotplug_read_trylock to always fail and (2) block until the last
>> remaining in-kernel file_hotplug_read_unlock() has executed?
>
> Yes there is room for more optimization in the slow path.
> I haven't noticed being a problem yet so I figured I would start
> with stupid and simple.
Yup, just wanted to point it out.
On Tue, Jun 2, 2009 at 9:51 AM, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
> I can easily see two passes. The first setting the flag an calling
> f_op->dead. The second some kind of consolidate walk through the task
> list, allowing checking on multiple files at once.
>
> I'm not ready to consider anything that will add cost to the fast
> path in the file descriptors though.
Makes sense.
Pekka
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