ratelimit.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * ratelimit.c - Do something with rate limit.
  4 *
  5 * Isolated from kernel/printk.c by Dave Young <hidave.darkstar@gmail.com>
  6 *
  7 * 2008-05-01 rewrite the function and use a ratelimit_state data struct as
  8 * parameter. Now every user can use their own standalone ratelimit_state.
  9 */
 10
 11#include <linux/ratelimit.h>
 12#include <linux/jiffies.h>
 13#include <linux/export.h>
 14
 15/*
 16 * __ratelimit - rate limiting
 17 * @rs: ratelimit_state data
 18 * @func: name of calling function
 19 *
 20 * This enforces a rate limit: not more than @rs->burst callbacks
 21 * in every @rs->interval
 22 *
 23 * RETURNS:
 24 * 0 means callbacks will be suppressed.
 25 * 1 means go ahead and do it.
 26 */
 27int ___ratelimit(struct ratelimit_state *rs, const char *func)
 28{
 29	/* Paired with WRITE_ONCE() in .proc_handler().
 30	 * Changing two values separately could be inconsistent
 31	 * and some message could be lost.  (See: net_ratelimit_state).
 32	 */
 33	int interval = READ_ONCE(rs->interval);
 34	int burst = READ_ONCE(rs->burst);
 35	unsigned long flags;
 36	int ret = 0;
 37
 38	/*
 39	 * Zero interval says never limit, otherwise, non-positive burst
 40	 * says always limit.
 41	 */
 42	if (interval <= 0 || burst <= 0) {
 43		WARN_ONCE(interval < 0 || burst < 0, "Negative interval (%d) or burst (%d): Uninitialized ratelimit_state structure?\n", interval, burst);
 44		ret = interval == 0 || burst > 0;
 45		if (!(READ_ONCE(rs->flags) & RATELIMIT_INITIALIZED) || (!interval && !burst) ||
 46		    !raw_spin_trylock_irqsave(&rs->lock, flags))
 47			goto nolock_ret;
 48
 49		/* Force re-initialization once re-enabled. */
 50		rs->flags &= ~RATELIMIT_INITIALIZED;
 51		goto unlock_ret;
 52	}
 53
 54	/*
 55	 * If we contend on this state's lock then just check if
 56	 * the current burst is used or not. It might cause
 57	 * false positive when we are past the interval and
 58	 * the current lock owner is just about to reset it.
 59	 */
 60	if (!raw_spin_trylock_irqsave(&rs->lock, flags)) {
 61		if (READ_ONCE(rs->flags) & RATELIMIT_INITIALIZED &&
 62		    atomic_read(&rs->rs_n_left) > 0 && atomic_dec_return(&rs->rs_n_left) >= 0)
 63			ret = 1;
 64		goto nolock_ret;
 65	}
 66
 67	if (!(rs->flags & RATELIMIT_INITIALIZED)) {
 68		rs->begin = jiffies;
 69		rs->flags |= RATELIMIT_INITIALIZED;
 70		atomic_set(&rs->rs_n_left, rs->burst);
 71	}
 72
 73	if (time_is_before_jiffies(rs->begin + interval)) {
 74		int m;
 75
 76		/*
 77		 * Reset rs_n_left ASAP to reduce false positives
 78		 * in parallel calls, see above.
 79		 */
 80		atomic_set(&rs->rs_n_left, rs->burst);
 81		rs->begin = jiffies;
 82
 83		if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE)) {
 84			m = ratelimit_state_reset_miss(rs);
 85			if (m) {
 86				printk_deferred(KERN_WARNING
 87						"%s: %d callbacks suppressed\n", func, m);
 88			}
 89		}
 90	}
 91
 92	/* Note that the burst might be taken by a parallel call. */
 93	if (atomic_read(&rs->rs_n_left) > 0 && atomic_dec_return(&rs->rs_n_left) >= 0)
 94		ret = 1;
 95
 96unlock_ret:
 97	raw_spin_unlock_irqrestore(&rs->lock, flags);
 98
 99nolock_ret:
100	if (!ret)
101		ratelimit_state_inc_miss(rs);
102
103	return ret;
104}
105EXPORT_SYMBOL(___ratelimit);