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Date: Tue, 28 Jan 2020 00:23:53 +0100
From: Alexey Gladkov <>
To: Linus Torvalds <>
Cc: LKML <>,
	Kernel Hardening <>,
	Linux API <>,
	Linux FS Devel <>,
	Linux Security Module <>,
	Akinobu Mita <>,
	Alexander Viro <>,
	Alexey Dobriyan <>,
	Andrew Morton <>,
	Andy Lutomirski <>,
	Daniel Micay <>,
	Djalal Harouni <>,
	"Dmitry V . Levin" <>,
	"Eric W . Biederman" <>,
	Greg Kroah-Hartman <>,
	Ingo Molnar <>,
	"J . Bruce Fields" <>,
	Jeff Layton <>,
	Jonathan Corbet <>, Kees Cook <>,
	Oleg Nesterov <>,
	Solar Designer <>,
	Stephen Rothwell <>
Subject: Re: [PATCH v7 07/11] proc: flush task dcache entries from all procfs

On Sat, Jan 25, 2020 at 10:45:25AM -0800, Linus Torvalds wrote:
> On Sat, Jan 25, 2020 at 5:06 AM Alexey Gladkov <> 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?

I’m 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

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