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

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Date:	Sun, 3 Mar 2013 19:32:23 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	David Miller <davem@...emloft.net>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC][PATCH] making vfree() safe from interrupt contexts

On Sun, Mar 03, 2013 at 06:47:36PM +0000, Al Viro 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'm not sure which tree should it go through, though.  Suggestions?
> The reason I'm interested in this sucker is the mess in fs/file.c (fdtable
> freeing), but the main change here is in mm/vmalloc.c...
> 
> 	Note that the patch obviously ought to be split - mm/vmalloc.c
> part, allowing vfree() in interrupt contexts (current mainline has
> BUG_ON() triggered in that case) and a chunk for each ad-hoc vfree()
> deferral scheme killed.
> 
> 	Comments?

BTW, looking a bit more shows another place that might benefit from that -
kernel/events/ring_buffer.c:rb_free_work() is called via schedule_work()
and I don't see anything in it besides vfree() that would demand that
kind of treatment.
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