From: Jeff Garzik <jgarzik@pobox.com>
To: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
Bartlomiej Zolnierkiewicz <B.Zolnierkiewicz@elka.pw.edu.pl>,
Douglas Gilbert <dougg@torque.net>, Jens Axboe <axboe@suse.de>,
William Lee Irwin III <wli@holomorphy.com>
Subject: Re: [PATCH 2.4] the perils of kunmap_atomic
Date: Thu, 28 Oct 2004 00:18:01 -0400 [thread overview]
Message-ID: <418072F9.2020004@pobox.com> (raw)
In-Reply-To: <20041027161936.GC1081@logos.cnet>
Marcelo Tosatti wrote:
> On Tue, Oct 26, 2004 at 07:31:24PM -0400, Jeff Garzik wrote:
>
>>kunmap_atomic() violates the Principle of Least Surprise in a nasty way.
>> kmap(), kunmap(), and kmap_atomic() all take struct page* to
>>reference the memory location. kunmap_atomic() is the oddball of the
>>three, and takes a kernel address.
>>
>>Ignoring the driver-related bugs that are present due to
>>kunmap_atomic()'s weirdness, there also appears to be a big in the
>>!CONFIG_HIGHMEM implementation in 2.4.x.
>>
>>(Bart is poking through some of the 2.6.x-related kunmap_atomic slip-ups)
>>
>>Anyway, what do people think about the attached patch to 2.4.x? I'm
>>surprised it has gone unnoticed until now.
>>
>> Jeff
>>
>>===== include/linux/highmem.h 1.12 vs edited =====
>>--- 1.12/include/linux/highmem.h 2003-06-30 20:18:42 -04:00
>>+++ edited/include/linux/highmem.h 2004-10-26 19:26:14 -04:00
>>@@ -70,7 +70,7 @@
>> #define kunmap(page) do { } while (0)
>>
>> #define kmap_atomic(page,idx) kmap(page)
>>-#define kunmap_atomic(page,idx) kunmap(page)
>>+#define kunmap_atomic(addr,idx) kunmap(virt_to_page(addr))
>>
>> #define bh_kmap(bh) ((bh)->b_data)
>> #define bh_kunmap(bh) do { } while (0)
>
>
> Ugh :(
Actually, a private email to me pointed out the obvious... kmap/kunmap
are no-ops on !CONFIG_HIGHMEM, so it's really a cosmetic bug, and my
patch won't fix anything but human confusion :)
> An audit of kunmap_atomic() users is needed.
agreed
Jeff
prev parent reply other threads:[~2004-10-28 4:18 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-10-26 23:31 Jeff Garzik
2004-10-26 23:36 ` Nigel Cunningham
2004-10-28 4:20 ` Jeff Garzik
2004-10-26 23:42 ` Nigel Cunningham
2004-10-27 0:07 ` William Lee Irwin III
2004-10-27 16:19 ` Marcelo Tosatti
2004-10-28 4:18 ` Jeff Garzik [this message]
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