From: Wu Fengguang <wfg@linux.intel.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Илья Тумайкин" <librarian_rus@yahoo.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-fsdevel@vger.kernel.org
Subject: Re: A regression in recent 3.2 kernel: bdi_dirty_limit() divide error
Date: Mon, 9 Jan 2012 12:04:45 +0800 [thread overview]
Message-ID: <20120109040445.GB31049@localhost> (raw)
In-Reply-To: <1326017954.2442.35.camel@twins>
[-- Attachment #1: Type: text/plain, Size: 461 bytes --]
On Sun, Jan 08, 2012 at 11:19:14AM +0100, Peter Zijlstra wrote:
> But even then, we limit PROP_MAX_SHIFT to 3*BITS_PER_LONG/4, I don't
> think that could ever overflow.
do_div() only uses the lower 32 bit value of the 64 bit denominator,
which may happen to be 0.
The denominator is not really 64 bit, but limited by PROP_MAX_SHIFT =
48 bit, however that upper limit looks not enough.
Ilya, would you help try the attached patch instead?
Thanks,
Fengguang
[-- Attachment #2: proportion-max-shift.patch --]
[-- Type: text/x-diff, Size: 755 bytes --]
Subject:
Date: Mon Jan 09 11:53:50 CST 2012
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
include/linux/proportions.h | 4 ++++
1 file changed, 4 insertions(+)
--- linux.orig/include/linux/proportions.h 2012-01-09 11:51:19.000000000 +0800
+++ linux/include/linux/proportions.h 2012-01-09 11:53:47.000000000 +0800
@@ -81,7 +81,11 @@ void prop_inc_percpu(struct prop_descrip
* Limit the time part in order to ensure there are some bits left for the
* cycle counter and fraction multiply.
*/
+#if BITS_PER_LONG == 32
#define PROP_MAX_SHIFT (3*BITS_PER_LONG/4)
+#else
+#define PROP_MAX_SHIFT (BITS_PER_LONG/2)
+#endif
#define PROP_FRAC_SHIFT (BITS_PER_LONG - PROP_MAX_SHIFT - 1)
#define PROP_FRAC_BASE (1UL << PROP_FRAC_SHIFT)
next prev parent reply other threads:[~2012-01-09 4:07 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1325884395.57034.YahooMailClassic@web161605.mail.bf1.yahoo.com>
2012-01-07 14:56 ` A regression in recent 3.2 kernel: bdi_dirty_limit() divide error Wu Fengguang
2012-01-07 16:35 ` Peter Zijlstra
2012-01-08 2:33 ` Wu Fengguang
2012-01-08 10:19 ` Peter Zijlstra
2012-01-09 4:04 ` Wu Fengguang [this message]
[not found] ` <1326205945.62365.YahooMailClassic@web161603.mail.bf1.yahoo.com>
2012-01-10 14:38 ` Wu Fengguang
2012-01-10 14:38 ` Wu Fengguang
2012-01-09 4:55 ` Wu Fengguang
2012-01-10 14:54 ` [PATCH] lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel Wu Fengguang
2012-01-10 15:01 ` Wu Fengguang
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