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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 7 Apr 2020 14:30:56 -0700
Message-ID: <CAHk-=whrZLs=+VkBXS_KWrMwoM2PRmw6mKEPJHRBQ_e3raFh9Q@mail.gmail.com>
Subject: Re: [PATCH v3] mm: Add kvfree_sensitive() for freeing sensitive data objects
To:     Uladzislau Rezki <urezki@gmail.com>
Cc:     Waiman Long <longman@redhat.com>, Joe Perches <joe@perches.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Howells <dhowells@redhat.com>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Linux-MM <linux-mm@kvack.org>, keyrings@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        David Rientjes <rientjes@google.com>
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On Tue, Apr 7, 2020 at 2:25 PM Uladzislau Rezki <urezki@gmail.com> wrote:
>
> Seems like there is only one place where we can "sleep". I mean when we
> call vfree(). That is free_vmap_area_noflush() -> try_purge_vmap_area_lazy().
> Basically try_purge_vmap_area_lazy() can call the schedule() what is not
> allowed for IRQs. Instead of inlining the try_purge_vmap_area_lazy()
> into current context we can schedule_work(). And i think it makes sense
> from many point of views.

I don't think that's the only case.

Or rather, that may be the only case of _sleeping_, but we also aren't
irq-safe wrt locking.

And I'm not just talking about the vmap_purge_lock mutex, but all the
spinlocks etc we have.

That said, I haven't looked at that code in _ages_. Maybe those things
would be trivial to just turn into irq-safe ones and there are no real
latency issues anywhere.

                Linus