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infra: fix limiter underflow 

Credits to Daniel Hermann for revealing this bug.
This commit is contained in:
Thomas Schoebel-Theuer 2013-07-15 09:58:35 +02:00
parent 5eae58a3a4
commit dae1218c50
2 changed files with 20 additions and 6 deletions
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24
kernel/lib_limiter.c
View File

@ -16,8 +16,17 @@ int mars_limit(struct mars_limiter *lim, int amount)
* down to the root of the hierarchy tree.
*/
while (lim != NULL) {
if (likely(lim->lim_stamp)) {
long long elapsed = now - lim->lim_stamp;
long long elapsed = now - lim->lim_stamp;
/* Sometimes, raw CPU clocks may do weired things...
*/
if (unlikely(elapsed <= 0))
elapsed = 1;
/* Only use incremental accumulation at repeated calls, but
* never after longer pauses.
*/
if (likely(lim->lim_stamp && elapsed < LIMITER_TIME_RESOLUTION * 8)) {
long long rate_raw;
int rate;
/* Races are possible, but taken into account.
@ -26,7 +35,11 @@ int mars_limit(struct mars_limiter *lim, int amount)
if (likely(amount > 0))
lim->lim_accu += amount;
rate = (long long)lim->lim_accu * LIMITER_TIME_RESOLUTION / elapsed;
rate_raw = lim->lim_accu * LIMITER_TIME_RESOLUTION / elapsed;
rate = rate_raw;
if (unlikely(rate_raw > INT_MAX)) {
rate = INT_MAX;
}
lim->lim_rate = rate;
// limit exceeded?
@ -40,8 +53,9 @@ int mars_limit(struct mars_limiter *lim, int amount)
elapsed -= LIMITER_TIME_RESOLUTION * 2;
if (elapsed > LIMITER_TIME_RESOLUTION) {
lim->lim_stamp += elapsed;
if (lim->lim_accu > 0) {
lim->lim_accu -= (long long)lim->lim_max_rate * elapsed / LIMITER_TIME_RESOLUTION;
lim->lim_accu -= (unsigned long long)lim->lim_rate * (unsigned long long)elapsed / LIMITER_TIME_RESOLUTION;
if (lim->lim_accu < 0) {
lim->lim_accu = 0;
}
}
} else {

2
kernel/lib_limiter.h
View File

@ -17,7 +17,7 @@ struct mars_limiter {
int lim_rate;
long long lim_stamp;
/* internal */
int lim_accu;
long long lim_accu;
};
extern int mars_limit(struct mars_limiter *lim, int amount);