linux-kernel - Re: 2.6.23-rc1: BUG_ON in kmap_atomic

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Message-ID: <e9c3a7c20707240655j533f0882xe067903e5f0ac9b7@mail.gmail.com>
Date:	Tue, 24 Jul 2007 06:55:36 -0700
From:	"Dan Williams" <dan.j.williams@...el.com>
To:	"Jens Axboe" <jens.axboe@...cle.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Alexey Dobriyan" <adobriyan@...il.com>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	mark.fasheh@...cle.com
Subject: Re: 2.6.23-rc1: BUG_ON in kmap_atomic_prot()

On 7/24/07, Jens Axboe <jens.axboe@...cle.com> wrote:
> What about the new async crypto stuff? I've been looking, but is it
> guarenteed that async_memcpy() runs in process context with interrupts
> enabled always? If not, there's a km type bug there.
>

Currently the only user is the MD raid456 driver, and yes, it only
performs copies from the handle_stripe routine which is always run in
process context with interrupts enabled.  However this is not
documented.  Would it be advisable to add a WARN_ON for this
condition?

> In general, I think the highmem stuff could do with more safety checks:
>
> - People ALWAYS get the atomic unmaps wrong, passing in the page instead
>   of the address. I've seen tons of these. And since kunmap_atomic()
>   takes a void pointer, nobody notices until it goes boom.
> - People easily get the km type wrong - they use KM_USERx in interrupt
>   context, or one of the irq variants without disabling interrupts.
>
> If we could just catch these two types of bugs, we've got a lot of these
> problems covered.
>
>
> --
> Jens Axboe
>
--
Dan
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