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| author | Michael Dalton <mwdalton@google.com> | 2014-01-16 22:23:29 -0800 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2014-01-16 23:46:06 -0800 |
| commit | 03144b5869d2921dafbea477246aeb5d4eb5fc38 (patch) | |
| tree | c0326022d8ccf711afb495c9c556447dfcf845b7 /lib | |
| parent | a953be53ce40440acb4740edb48577b9468d4c3d (diff) | |
| download | linux-03144b5869d2921dafbea477246aeb5d4eb5fc38.tar.gz linux-03144b5869d2921dafbea477246aeb5d4eb5fc38.tar.bz2 linux-03144b5869d2921dafbea477246aeb5d4eb5fc38.zip | |
lib: Ensure EWMA does not store wrong intermediate values
To ensure ewma_read() without a lock returns a valid but possibly
out of date average, modify ewma_add() by using ACCESS_ONCE to prevent
intermediate wrong values from being written to avg->internal.
Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Michael Dalton <mwdalton@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/average.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/lib/average.c b/lib/average.c index 99a67e662b3c..114d1beae0c7 100644 --- a/lib/average.c +++ b/lib/average.c @@ -53,8 +53,10 @@ EXPORT_SYMBOL(ewma_init); */ struct ewma *ewma_add(struct ewma *avg, unsigned long val) { - avg->internal = avg->internal ? - (((avg->internal << avg->weight) - avg->internal) + + unsigned long internal = ACCESS_ONCE(avg->internal); + + ACCESS_ONCE(avg->internal) = internal ? + (((internal << avg->weight) - internal) + (val << avg->factor)) >> avg->weight : (val << avg->factor); return avg; |