This is a note to let you know that I've just added the patch titled
lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel
to the 3.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
lib-proportion-lower-prop_max_shift-to-32-on-64-bit-kernel.patch
and it can be found in the queue-3.2 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 3310225dfc71a35a2cc9340c15c0e08b14b3c754 Mon Sep 17 00:00:00 2001
From: Wu Fengguang <[email protected]>
Date: Mon, 9 Jan 2012 11:53:50 -0600
Subject: lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel
From: Wu Fengguang <[email protected]>
commit 3310225dfc71a35a2cc9340c15c0e08b14b3c754 upstream.
PROP_MAX_SHIFT should be set to <=32 on 64-bit box. This fixes two bugs
in the below lines of bdi_dirty_limit():
bdi_dirty *= numerator;
do_div(bdi_dirty, denominator);
1) divide error: do_div() only uses the lower 32 bit of the denominator,
which may trimmed to be 0 when PROP_MAX_SHIFT > 32.
2) overflow: (bdi_dirty * numerator) could easily overflow if numerator
used up to 48 bits, leaving only 16 bits to bdi_dirty
Cc: Peter Zijlstra <[email protected]>
Reported-by: Ilya Tumaykin <[email protected]>
Tested-by: Ilya Tumaykin <[email protected]>
Signed-off-by: Wu Fengguang <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
include/linux/proportions.h | 4 ++++
1 file changed, 4 insertions(+)
--- a/include/linux/proportions.h
+++ b/include/linux/proportions.h
@@ -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)
Patches currently in stable-queue which might be from [email protected] are
queue-3.2/writeback-fix-dereferencing-null-bdi-dev-on-trace_writeback_queue.patch
queue-3.2/lib-proportion-lower-prop_max_shift-to-32-on-64-bit-kernel.patch
queue-3.2/writeback-fix-null-bdi-dev-in-trace-writeback_single_inode.patch
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