Re: printk_ratelimit and net_ratelimit conflict and tunable behavior

David Miller
2008-02-21T06:31:55Z

From: "Hawkes Steve-FSH016" <Steve.Hawkes@motorola.com>
Date: Tue, 19 Feb 2008 15:30:51 -0600

[ netdev CC:'d ]

> The printk_ratelimit() and net_ratelimit() functions are coupled and
> interfere with each other. Each has their own tunable parameters to
> control their respective rate limiting feature, but they share common
> state variables, causing the rate limiting to behave in an unexpected
> fashion when the tunables for each are set to different values.
>
> Also, changes to rate limiting tunable parameters do not always take
> effect
> properly since state is not recomputed when changes occur. For example,
> if
> the ratelimit_burst tunable value is increased while rate limiting
> is occurring, the change doesn't take full effect until at least enough
> time between messages occurs so that the toks value reaches
> ratelimit_burst * ratelimit_jiffies. This can result in messages being
> suppressed when they should be allowed.

This looks fine to me, please provide a proper "Signed-off-by: " as
described in linux/Documentation/SubmittingPatches

Thanks.

> diff -Naup OLD/include/linux/kernel.h NEW/include/linux/kernel.h
> --- OLD/include/linux/kernel.h 2008-02-19 10:02:07.461496000 -0600
> +++ NEW/include/linux/kernel.h 2008-02-19 10:45:32.858306000 -0600
> @@ -196,8 +196,20 @@ static inline int log_buf_copy(char *des
>
> unsigned long int_sqrt(unsigned long);
>
> +struct printk_ratelimit_state
> +{
> + unsigned long toks;
> + unsigned long last_jiffies;
> + int missed;
> + int limit_jiffies;
> + int limit_burst;
> + char const *facility;
> +};
> +
> +extern int __printk_ratelimit(int ratelimit_jiffies,
> + int ratelimit_burst,
> + struct printk_ratelimit_state *state);
> extern int printk_ratelimit(void);
> -extern int __printk_ratelimit(int ratelimit_jiffies, int
> ratelimit_burst);
> extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,
> unsigned int interval_msec);
>
> diff -Naup OLD/net/core/utils.c NEW/net/core/utils.c
> --- OLD/net/core/utils.c 2008-02-19 10:01:26.442370000 -0600
> +++ NEW/net/core/utils.c 2008-02-19 10:46:45.026731000 -0600
> @@ -41,7 +41,18 @@ EXPORT_SYMBOL(net_msg_warn);
> */
> int net_ratelimit(void)
> {
> - return __printk_ratelimit(net_msg_cost, net_msg_burst);
> + static struct printk_ratelimit_state limit_state = {
> + .toks = 10 * 5 * HZ,
> + .last_jiffies = 0,
> + .missed = 0,
> + .limit_jiffies = 5 * HZ,
> + .limit_burst = 10,
> + .facility = "net"
> + };
> +
> + return __printk_ratelimit(net_msg_cost,
> + net_msg_burst,
> + &limit_state);
> }
> EXPORT_SYMBOL(net_ratelimit);
>
> diff -Naup OLD/kernel/printk.c NEW/kernel/print.c
> --- OLD/kernel/printk.c 2008-02-19 10:00:47.359068000 -0600
> +++ NEW/kernel/printk.c 2008-02-19 10:46:30.748743000 -0600
> @@ -1236,37 +1236,47 @@ void tty_write_message(struct tty_struct
> }
>
> /*
> - * printk rate limiting, lifted from the networking subsystem.
> + * printk rate limiting.
> *
> - * This enforces a rate limit: not more than one kernel message
> - * every printk_ratelimit_jiffies to make a denial-of-service
> - * attack impossible.
> + * This enforces a rate limit to mitigate denial-of-service attacks:
> + * not more than ratelimit_burst messages every ratelimit_jiffies.
> */
> -int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
> +int __printk_ratelimit(int ratelimit_jiffies,
> + int ratelimit_burst,
> + struct printk_ratelimit_state *state)
> {
> static DEFINE_SPINLOCK(ratelimit_lock);
> - static unsigned long toks = 10 * 5 * HZ;
> - static unsigned long last_msg;
> - static int missed;
> unsigned long flags;
> unsigned long now = jiffies;
>
> spin_lock_irqsave(&ratelimit_lock, flags);
> - toks += now - last_msg;
> - last_msg = now;
> - if (toks > (ratelimit_burst * ratelimit_jiffies))
> - toks = ratelimit_burst * ratelimit_jiffies;
> - if (toks >= ratelimit_jiffies) {
> - int lost = missed;
> -
> - missed = 0;
> - toks -= ratelimit_jiffies;
> + state->toks += now - state->last_jiffies;
> + /* Reset limiting if tunables changed */
> + if ((state->limit_jiffies != ratelimit_jiffies) ||
> + (state->limit_burst != ratelimit_burst)) {
> + state->toks = ratelimit_burst * ratelimit_jiffies;
> + state->limit_jiffies = ratelimit_jiffies;
> + state->limit_burst = ratelimit_burst;
> + }
> + state->last_jiffies = now;
> + if (state->toks > (ratelimit_burst * ratelimit_jiffies))
> + state->toks = ratelimit_burst * ratelimit_jiffies;
> + if (state->toks >= ratelimit_jiffies) {
> + int lost = state->missed;
> + state->missed = 0;
> + state->toks -= ratelimit_jiffies;
> spin_unlock_irqrestore(&ratelimit_lock, flags);
> - if (lost)
> - printk(KERN_WARNING "printk: %d messages
> suppressed.\n", lost);
> + if (lost) {
> + printk(KERN_WARNING
> + "printk: %d %s%smessage%s suppressed.\n",
> + lost,
> + (state->facility == 0 ? "" :
> state->facility),
> + (state->facility == 0 ? "" : " "),
> + (lost > 1 ? "s" : ""));
> + }
> return 1;
> }
> - missed++;
> + state->missed++;
> spin_unlock_irqrestore(&ratelimit_lock, flags);
> return 0;
> }
> @@ -1280,8 +1290,18 @@ int printk_ratelimit_burst = 10;
>
> int printk_ratelimit(void)
> {
> + static struct printk_ratelimit_state limit_state = {
> + .toks = 10 * 5 * HZ,
> + .last_jiffies = 0,
> + .missed = 0,
> + .limit_jiffies = 5 * HZ,
> + .limit_burst = 10,
> + .facility = 0
> + };
> +
> return __printk_ratelimit(printk_ratelimit_jiffies,
> - printk_ratelimit_burst);
> + printk_ratelimit_burst,
> + &limit_state);
> }
> EXPORT_SYMBOL(printk_ratelimit);
>
> --
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