Re: [PATCH v7 07/11] proc: flush task dcache entries from all procfs instances

[Alexey Gladkov]

On Sat, Jan 25, 2020 at 10:45:25AM -0800, Linus Torvalds wrote:
> On Sat, Jan 25, 2020 at 5:06 AM Alexey Gladkov <gladkov.alexey@xxxxxxxxx> wrote:
> >
> > This allows to flush dcache entries of a task on multiple procfs mounts
> > per pid namespace.
> 
> From a quick read-through, this is the only one I really react negatively to.
> 
> The locking looks odd. It only seems to protect the new proc_mounts
> list, but then it's a whole big rwsem, and it's taken over all of
> proc_flush_task_mnt(), and the locking is exported to all over as a
> result of that - including the dummy functions for "there is no proc"
> case.
> 
> And proc_flush_task_mnt() itself should need no locking over any of
> it, so it's all just for the silly looping over the list.

Thank you, I will rework this part.

> So
> 
>  (a) this looks fishy and feels wrong - I get a very strong feeling
> that the locking is wrong to begin with, and could/should have been
> done differently
> 
>  (b) all the locking should have been internal to /proc, and those
> wrappers shouldn't exist in a common header file (and certainly not
> for the non-proc case).
> 
> Yes, (a) is just a feeling, and I don't have any great suggestions.
> Maybe make it an RCU list and use a spinlock for updating it?

Iâm thinking, is it possible to get rid of proc_flush_task at all ?
Maybe we can try to flush dcache during readdir for example.

> But (b) is pretty much a non-starter in this form. Those wrappers
> shouldn't be in a globally exported core header file. No way.
> 
>                Linus
> 

-- 
Rgrds, legion