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Message-ID: <1531789154.18720.3.camel@arista.com>
Date: Tue, 17 Jul 2018 01:59:14 +0100
From: Dmitry Safonov <dima@...sta.com>
To: linux-kernel@...r.kernel.org
Cc: Andy Shevchenko <andy.shevchenko@...il.com>,
Arnd Bergmann <arnd@...db.de>, David Airlie <airlied@...ux.ie>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jani Nikula <jani.nikula@...ux.intel.com>,
Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
Rodrigo Vivi <rodrigo.vivi@...el.com>,
Theodore Ts'o <tytso@....edu>,
Thomas Gleixner <tglx@...utronix.de>,
intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCHv3] lib/ratelimit: Lockless ratelimiting
I would be glad if someone helps/bothers to review the change :C
Thanks,
Dmitry
On Tue, 2018-07-03 at 23:56 +0100, Dmitry Safonov wrote:
> 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@...sta.com>
>
> Dropped `name' in as it's unused in RATELIMIT_STATE_INIT()
>
> Cc: Andy Shevchenko <andy.shevchenko@...il.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: David Airlie <airlied@...ux.ie>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Jani Nikula <jani.nikula@...ux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@...el.com>
> Cc: "Theodore Ts'o" <tytso@....edu>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: intel-gfx@...ts.freedesktop.org
> Cc: dri-devel@...ts.freedesktop.org
> Signed-off-by: Dmitry Safonov <dima@...sta.com>
> ---
> drivers/char/random.c | 28 ++++++++-----------
> drivers/gpu/drm/i915/i915_perf.c | 8 ++++--
> fs/btrfs/super.c | 16 +++++------
> fs/xfs/scrub/scrub.c | 2 +-
> include/linux/ratelimit.h | 31 ++++++++++++---------
> kernel/user.c | 2 +-
> lib/ratelimit.c | 59 +++++++++++++++++++-----------
> ----------
> 7 files changed, 73 insertions(+), 73 deletions(-)
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index cd888d4ee605..0be31b3eadab 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -439,10 +439,8 @@ static void _crng_backtrack_protect(struct
> crng_state *crng,
> static void process_random_ready_list(void);
> static void _get_random_bytes(void *buf, int nbytes);
>
> -static struct ratelimit_state unseeded_warning =
> - RATELIMIT_STATE_INIT("warn_unseeded_randomness", HZ, 3);
> -static struct ratelimit_state urandom_warning =
> - RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3);
> +static struct ratelimit_state unseeded_warning =
> RATELIMIT_STATE_INIT(HZ, 3);
> +static struct ratelimit_state urandom_warning =
> RATELIMIT_STATE_INIT(HZ, 3);
>
> static int ratelimit_disable __read_mostly;
>
> @@ -937,24 +935,22 @@ 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) {
> + unsigned 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) {
> - 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) {
> - pr_notice("random: %d urandom warning(s)
> missed "
> - "due to ratelimiting\n",
> - urandom_warning.missed);
> - urandom_warning.missed = 0;
> - }
> + unseeded_miss =
> atomic_xchg(&unseeded_warning.missed, 0);
> + if (unseeded_miss)
> + pr_notice("random: %u get_random_xx
> warning(s) missed "
> + "due to ratelimiting\n",
> unseeded_miss);
> + urandom_miss = atomic_xchg(&urandom_warning.missed,
> 0);
> + if (urandom_miss)
> + pr_notice("random: %u urandom warning(s)
> missed "
> + "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..dcfba3023547 100644
> --- a/drivers/gpu/drm/i915/i915_perf.c
> +++ b/drivers/gpu/drm/i915/i915_perf.c
> @@ -1295,6 +1295,7 @@ free_oa_buffer(struct drm_i915_private *i915)
> static void i915_oa_stream_destroy(struct i915_perf_stream *stream)
> {
> struct drm_i915_private *dev_priv = stream->dev_priv;
> + unsigned int msg_missed;
>
> BUG_ON(stream != dev_priv->perf.oa.exclusive_stream);
>
> @@ -1317,9 +1318,10 @@ 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) {
> - DRM_NOTE("%d spurious OA report notices suppressed
> due to ratelimiting\n",
> - dev_priv-
> >perf.oa.spurious_report_rs.missed);
> + msg_missed = atomic_read(&dev_priv-
> >perf.oa.spurious_report_rs.missed);
> + if (msg_missed) {
> + DRM_NOTE("%u spurious OA report notices suppressed
> due to ratelimiting\n",
> + msg_missed);
> }
> }
>
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 81107ad49f3a..ffab6c23bc50 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -177,14 +177,14 @@ static const char * const logtypes[] = {
> * messages doesn't cause more important ones to be dropped.
> */
> static struct ratelimit_state printk_limits[] = {
> - RATELIMIT_STATE_INIT(printk_limits[0],
> DEFAULT_RATELIMIT_INTERVAL, 100),
> - RATELIMIT_STATE_INIT(printk_limits[1],
> DEFAULT_RATELIMIT_INTERVAL, 100),
> - RATELIMIT_STATE_INIT(printk_limits[2],
> DEFAULT_RATELIMIT_INTERVAL, 100),
> - RATELIMIT_STATE_INIT(printk_limits[3],
> DEFAULT_RATELIMIT_INTERVAL, 100),
> - RATELIMIT_STATE_INIT(printk_limits[4],
> DEFAULT_RATELIMIT_INTERVAL, 100),
> - RATELIMIT_STATE_INIT(printk_limits[5],
> DEFAULT_RATELIMIT_INTERVAL, 100),
> - RATELIMIT_STATE_INIT(printk_limits[6],
> DEFAULT_RATELIMIT_INTERVAL, 100),
> - RATELIMIT_STATE_INIT(printk_limits[7],
> DEFAULT_RATELIMIT_INTERVAL, 100),
> + RATELIMIT_STATE_INIT(DEFAULT_RATELIMIT_INTERVAL, 100),
> + RATELIMIT_STATE_INIT(DEFAULT_RATELIMIT_INTERVAL, 100),
> + RATELIMIT_STATE_INIT(DEFAULT_RATELIMIT_INTERVAL, 100),
> + RATELIMIT_STATE_INIT(DEFAULT_RATELIMIT_INTERVAL, 100),
> + RATELIMIT_STATE_INIT(DEFAULT_RATELIMIT_INTERVAL, 100),
> + RATELIMIT_STATE_INIT(DEFAULT_RATELIMIT_INTERVAL, 100),
> + RATELIMIT_STATE_INIT(DEFAULT_RATELIMIT_INTERVAL, 100),
> + RATELIMIT_STATE_INIT(DEFAULT_RATELIMIT_INTERVAL, 100),
> };
>
> void btrfs_printk(const struct btrfs_fs_info *fs_info, const char
> *fmt, ...)
> diff --git a/fs/xfs/scrub/scrub.c b/fs/xfs/scrub/scrub.c
> index 58ae76b3a421..8b58b439694a 100644
> --- a/fs/xfs/scrub/scrub.c
> +++ b/fs/xfs/scrub/scrub.c
> @@ -349,7 +349,7 @@ xfs_scrub_experimental_warning(
> struct xfs_mount *mp)
> {
> static struct ratelimit_state scrub_warning =
> RATELIMIT_STATE_INIT(
> - "xfs_scrub_warning", 86400 * HZ, 1);
> + 86400 * HZ, 1);
> ratelimit_set_flags(&scrub_warning,
> RATELIMIT_MSG_ON_RELEASE);
>
> if (__ratelimit(&scrub_warning))
> diff --git a/include/linux/ratelimit.h b/include/linux/ratelimit.h
> index 8ddf79e9207a..f9a9386dd869 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
> @@ -13,38 +12,39 @@
> #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), \
> +#define RATELIMIT_STATE_INIT(interval_init, burst_init) {
> \
> .interval = interval_init,
> \
> .burst = burst_init,
> \
> + .printed = ATOMIC_INIT(0),
> \
> + .missed = ATOMIC_INIT(0),
> \
> }
>
> #define RATELIMIT_STATE_INIT_DISABLED
> \
> - RATELIMIT_STATE_INIT(ratelimit_state, 0,
> DEFAULT_RATELIMIT_BURST)
> + RATELIMIT_STATE_INIT(0, DEFAULT_RATELIMIT_BURST)
>
> #define DEFINE_RATELIMIT_STATE(name, interval_init, burst_init)
> \
>
> \
> struct ratelimit_state name =
> \
> - RATELIMIT_STATE_INIT(name, interval_init,
> burst_init) \
> + RATELIMIT_STATE_INIT(interval_init, burst_init)
>
> static inline void ratelimit_state_init(struct ratelimit_state *rs,
> int interval, int burst)
> {
> 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 +53,21 @@ 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) {
> + missed = atomic_xchg(&rs->missed, 0);
> + if (missed)
> 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/kernel/user.c b/kernel/user.c
> index 36288d840675..a964f842d8f0 100644
> --- a/kernel/user.c
> +++ b/kernel/user.c
> @@ -101,7 +101,7 @@ struct user_struct root_user = {
> .sigpending = ATOMIC_INIT(0),
> .locked_shm = 0,
> .uid = GLOBAL_ROOT_UID,
> - .ratelimit =
> RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
> + .ratelimit = RATELIMIT_STATE_INIT(0, 0),
> };
>
> /*
> diff --git a/lib/ratelimit.c b/lib/ratelimit.c
> index d01f47135239..d9b749d40108 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 int missed = 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);
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