linux-kernel - Re: [RFC][PATCH] making vfree() safe from interrupt contexts

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Date:	Sun, 3 Mar 2013 14:34:00 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [RFC][PATCH] making vfree() safe from interrupt contexts

On Sun, Mar 3, 2013 at 10:47 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
>         To bring back the thing discussed back in, IIRC, December: we have
> a bunch of places where inability to do vfree() from interrupt contexts
> (the most common case is doing that from RCU callback) leads to very
> ugly open-coded schemes that delay it one way or another.  We can let vfree()
> itself do that instead.  AFAICS, it works; the diff below covers several
> obvious cases found just by grep.  I'm fairly sure that there's more code
> that could benefit from that...

I have nothing against the patch, but I hate seeing it just before I
am getting ready to close the merge window.

And I'm not willing to apply it, since I think it's buggy: the whole
point of deferred_vfree() is that it is for irq context, yet it's not
using an irq-safe lock. So nested interrupts can deadlock.

So I think the concept is fine, the patch is probably fine after just
changing the spinlock to be irq-safe, but the timing is horrible. It
doesn't seem to be *that* urgent, so maybe you could just put it in
your queue for 3.10 after fixing the irq locking?

            Linus
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