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authorWu Fengguang <fengguang.wu@intel.com>2012-01-09 11:53:50 -0600
committerWu Fengguang <fengguang.wu@intel.com>2012-02-01 16:53:46 +0800
commit3310225dfc71a35a2cc9340c15c0e08b14b3c754 (patch)
tree0475693eddb964dd8ea125e59f9e9efbcabd1dd0 /include
parent15eb77a07c714ac80201abd0a9568888bcee6276 (diff)
lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel
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: <stable@kernel.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Reported-by: Ilya Tumaykin <librarian_rus@yahoo.com> Tested-by: Ilya Tumaykin <librarian_rus@yahoo.com> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Diffstat (limited to 'include')
-rw-r--r--include/linux/proportions.h4
1 files changed, 4 insertions, 0 deletions
diff --git a/include/linux/proportions.h b/include/linux/proportions.h
index ef35bb73f69..26a8a4ed9b0 100644
--- a/include/linux/proportions.h
+++ b/include/linux/proportions.h
@@ -81,7 +81,11 @@ void prop_inc_percpu(struct prop_descriptor *pd, struct prop_local_percpu *pl)
* 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)