Currently ratelimit_state is protected with spin_lock. If the .lock is taken at the moment of ___ratelimit() call, the message is suppressed to make ratelimiting robust.
That results in the following issue issue: CPU0 CPU1 ------------------ ------------------ printk_ratelimit() printk_ratelimit() | | try_spin_lock() try_spin_lock() | | time_is_before_jiffies() return 0; // suppress
So, concurrent call of ___ratelimit() results in silently suppressing one of the messages, regardless if the limit is reached or not. And rc->missed is not increased in such case so the issue is covered from user.
Convert ratelimiting to use atomic counters and drop spin_lock.
Note: That might be unexpected, but with the first interval of messages storm one can print up to burst*2 messages. So, it doesn't guarantee that in *any* interval amount of messages is lesser than burst. But, that differs lightly from previous behavior where one can start burst=5 interval and print 4 messages on the last milliseconds of interval + new 5 messages from new interval (totally 9 messages in lesser than interval value):
msg0 msg1-msg4 msg0-msg4 | | | | | | |--o---------------------o-|-----o--------------------|--> (t) <-------> Lesser than burst
Dropped dev/random patch since v1 version: lkml.kernel.org/r/20180510125211.12583-1-dima@arista.com
Cc: Arnd Bergmann arnd@arndb.de Cc: David Airlie airlied@linux.ie Cc: Dmitry Safonov 0x7f454c46@gmail.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Jani Nikula jani.nikula@linux.intel.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Rodrigo Vivi rodrigo.vivi@intel.com Cc: "Theodore Ts'o" tytso@mit.edu Cc: Thomas Gleixner tglx@linutronix.de Cc: intel-gfx@lists.freedesktop.org Cc: dri-devel@lists.freedesktop.org Signed-off-by: Dmitry Safonov dima@arista.com --- drivers/char/random.c | 16 ++++------- drivers/gpu/drm/i915/i915_perf.c | 4 +-- include/linux/ratelimit.h | 24 +++++++++------- lib/ratelimit.c | 59 +++++++++++++++++++--------------------- 4 files changed, 50 insertions(+), 53 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c index a8fb0020ba5c..ba67ea0dc568 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -936,24 +936,20 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r) crng->init_time = jiffies; spin_unlock_irqrestore(&crng->lock, flags); if (crng == &primary_crng && crng_init < 2) { + int unseeded_miss, urandom_miss; + invalidate_batched_entropy(); numa_crng_init(); crng_init = 2; process_random_ready_list(); wake_up_interruptible(&crng_init_wait); pr_notice("random: crng init done\n"); - if (unseeded_warning.missed) { + if ((unseeded_miss = atomic_xchg(&unseeded_warning.missed, 0))) pr_notice("random: %d get_random_xx warning(s) missed " - "due to ratelimiting\n", - unseeded_warning.missed); - unseeded_warning.missed = 0; - } - if (urandom_warning.missed) { + "due to ratelimiting\n", unseeded_miss); + if ((urandom_miss = atomic_xchg(&urandom_warning.missed, 0))) pr_notice("random: %d urandom warning(s) missed " - "due to ratelimiting\n", - urandom_warning.missed); - urandom_warning.missed = 0; - } + "due to ratelimiting\n", urandom_miss); } }
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c index 019bd2d073ad..75f6203f6e8e 100644 --- a/drivers/gpu/drm/i915/i915_perf.c +++ b/drivers/gpu/drm/i915/i915_perf.c @@ -1317,9 +1317,9 @@ static void i915_oa_stream_destroy(struct i915_perf_stream *stream)
put_oa_config(dev_priv, stream->oa_config);
- if (dev_priv->perf.oa.spurious_report_rs.missed) { + if (atomic_read(&dev_priv->perf.oa.spurious_report_rs.missed)) { DRM_NOTE("%d spurious OA report notices suppressed due to ratelimiting\n", - dev_priv->perf.oa.spurious_report_rs.missed); + atomic_read(&dev_priv->perf.oa.spurious_report_rs.missed)); } }
diff --git a/include/linux/ratelimit.h b/include/linux/ratelimit.h index 8ddf79e9207a..7b5914e12d5b 100644 --- a/include/linux/ratelimit.h +++ b/include/linux/ratelimit.h @@ -4,7 +4,6 @@
#include <linux/param.h> #include <linux/sched.h> -#include <linux/spinlock.h>
#define DEFAULT_RATELIMIT_INTERVAL (5 * HZ) #define DEFAULT_RATELIMIT_BURST 10 @@ -13,20 +12,20 @@ #define RATELIMIT_MSG_ON_RELEASE BIT(0)
struct ratelimit_state { - raw_spinlock_t lock; /* protect the state */ + atomic_t printed; + atomic_t missed;
int interval; int burst; - int printed; - int missed; unsigned long begin; unsigned long flags; };
#define RATELIMIT_STATE_INIT(name, interval_init, burst_init) { \ - .lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock), \ .interval = interval_init, \ .burst = burst_init, \ + .printed = ATOMIC_INIT(0), \ + .missed = ATOMIC_INIT(0), \ }
#define RATELIMIT_STATE_INIT_DISABLED \ @@ -42,9 +41,10 @@ static inline void ratelimit_state_init(struct ratelimit_state *rs, { memset(rs, 0, sizeof(*rs));
- raw_spin_lock_init(&rs->lock); rs->interval = interval; rs->burst = burst; + atomic_set(&rs->printed, 0); + atomic_set(&rs->missed, 0); }
static inline void ratelimit_default_init(struct ratelimit_state *rs) @@ -53,16 +53,20 @@ static inline void ratelimit_default_init(struct ratelimit_state *rs) DEFAULT_RATELIMIT_BURST); }
+/* + * Keeping it simple: not reenterable and not safe for concurrent + * ___ratelimit() call as used only by devkmsg_release(). + */ static inline void ratelimit_state_exit(struct ratelimit_state *rs) { + int missed; + if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE)) return;
- if (rs->missed) { + if ((missed = atomic_xchg(&rs->missed, 0))) pr_warn("%s: %d output lines suppressed due to ratelimiting\n", - current->comm, rs->missed); - rs->missed = 0; - } + current->comm, missed); }
static inline void diff --git a/lib/ratelimit.c b/lib/ratelimit.c index d01f47135239..c99305e9239f 100644 --- a/lib/ratelimit.c +++ b/lib/ratelimit.c @@ -13,6 +13,18 @@ #include <linux/jiffies.h> #include <linux/export.h>
+static void ratelimit_end_interval(struct ratelimit_state *rs, const char *func) +{ + rs->begin = jiffies; + + if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE)) { + unsigned missed = (unsigned)atomic_xchg(&rs->missed, 0); + + if (missed) + pr_warn("%s: %u callbacks suppressed\n", func, missed); + } +} + /* * __ratelimit - rate limiting * @rs: ratelimit_state data @@ -27,45 +39,30 @@ */ int ___ratelimit(struct ratelimit_state *rs, const char *func) { - unsigned long flags; - int ret; - if (!rs->interval) return 1;
- /* - * If we contend on this state's lock then almost - * by definition we are too busy to print a message, - * in addition to the one that will be printed by - * the entity that is holding the lock already: - */ - if (!raw_spin_trylock_irqsave(&rs->lock, flags)) + if (unlikely(!rs->burst)) { + atomic_add_unless(&rs->missed, 1, -1); + if (time_is_before_jiffies(rs->begin + rs->interval)) + ratelimit_end_interval(rs, func); + return 0; + }
- if (!rs->begin) - rs->begin = jiffies; + if (atomic_add_unless(&rs->printed, 1, rs->burst)) + return 1;
if (time_is_before_jiffies(rs->begin + rs->interval)) { - if (rs->missed) { - if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE)) { - printk_deferred(KERN_WARNING - "%s: %d callbacks suppressed\n", - func, rs->missed); - rs->missed = 0; - } - } - rs->begin = jiffies; - rs->printed = 0; - } - if (rs->burst && rs->burst > rs->printed) { - rs->printed++; - ret = 1; - } else { - rs->missed++; - ret = 0; + if (atomic_cmpxchg(&rs->printed, rs->burst, 0)) + ratelimit_end_interval(rs, func); } - raw_spin_unlock_irqrestore(&rs->lock, flags);
- return ret; + if (atomic_add_unless(&rs->printed, 1, rs->burst)) + return 1; + + atomic_add_unless(&rs->missed, 1, -1); + + return 0; } EXPORT_SYMBOL(___ratelimit);