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[PATCH] rcu: Fix sign bug making rcu_random always return the same sequence

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rcu_random uses a counter rrs_count to occasionally mix data from
get_random_bytes into the state of its pseudorandom generator.  However,
the rrs_counter gets declared as an unsigned long, and rcu_random checks
for --rrs_count < 0, so this code will never mix any real random data into
the state, and will thus always return the same sequence of random numbers.

Also, change the return value of rcu_random from long to unsigned long, to
avoid potential issues caused by the use of the % operator, which can
return negative values for negative left operands.

Signed-off-by: Josh Triplett <josh@freedesktop.org>
Acked-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Josh Triplett 2006-10-04 02:17:12 -07:00 committed by Linus Torvalds
parent 2860aaba4d
commit 75cfef32f2
1 changed files with 2 additions and 2 deletions
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4
kernel/rcutorture.c
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@ -147,7 +147,7 @@ rcu_torture_free(struct rcu_torture *p)
struct rcu_random_state { struct rcu_random_state {
unsigned long rrs_state; unsigned long rrs_state;
unsigned long rrs_count; long rrs_count;
}; };
#define RCU_RANDOM_MULT 39916801 /* prime */ #define RCU_RANDOM_MULT 39916801 /* prime */
@ -160,7 +160,7 @@ struct rcu_random_state {
* Crude but fast random-number generator. Uses a linear congruential * Crude but fast random-number generator. Uses a linear congruential
* generator, with occasional help from get_random_bytes(). * generator, with occasional help from get_random_bytes().
*/ */
static long static unsigned long
rcu_random(struct rcu_random_state *rrsp) rcu_random(struct rcu_random_state *rrsp)
{ {
long refresh; long refresh;