[RFC v2 2/2] scsi: add rate limit to scsi sense code uevent

[Song Liu]

This patch adds rate limits to SCSI sense code uevets. Currently,
the rate limit is hard-coded to 16 events per second.

The code tracks nano second time of latest 16 events in a circular
buffer. When a new event arrives, the time is compared against the
latest time in the buffer. If the difference is smaller than one
second, the new event is dropped.

Signed-off-by: Song Liu <songliubrav...@fb.com>
---
 drivers/scsi/scsi_error.c  | 15 +++++++++++++++
 drivers/scsi/scsi_scan.c   |  4 ++++
 include/scsi/scsi_device.h | 12 +++++++++++-
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index a49c63a..91e6b0a 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -436,11 +436,26 @@ static void scsi_send_sense_uevent(struct scsi_device 
*sdev,
 #ifdef CONFIG_SCSI_SENSE_UEVENT
        struct scsi_event *evt;
        unsigned char sb_len;
+       unsigned long flags;
+       u64 time_ns;
 
        if (!test_bit(sshdr->sense_key & 0xf,
                      &sdev->sense_event_filter))
                return;
        evt = sdev_evt_alloc(SDEV_EVT_SCSI_SENSE, GFP_ATOMIC);
+
+       time_ns = ktime_to_ns(ktime_get());
+       spin_lock_irqsave(&sdev->latest_event_lock, flags);
+       if (time_ns - sdev->latest_event_times[sdev->latest_event_idx] <
+           NSEC_PER_SEC) {
+               spin_unlock_irqrestore(&sdev->latest_event_lock, flags);
+               return;
+       }
+       sdev->latest_event_times[sdev->latest_event_idx] = time_ns;
+       sdev->latest_event_idx = (sdev->latest_event_idx + 1) %
+               MAX_SENSE_EVENT_PER_SECOND;
+       spin_unlock_irqrestore(&sdev->latest_event_lock, flags);
+
        if (!evt)
                return;
 
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 6f7128f..67b3f71 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -301,6 +301,10 @@ static struct scsi_device *scsi_alloc_sdev(struct 
scsi_target *starget,
                }
        }
 
+#ifdef CONFIG_SCSI_SENSE_UEVENT
+       spin_lock_init(&sdev->latest_event_lock);
+#endif
+
        return sdev;
 
 out_device_destroy:
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 5b6f06d..9217dae 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -214,12 +214,22 @@ struct scsi_device {
        atomic_t ioerr_cnt;
 
 #ifdef CONFIG_SCSI_SENSE_UEVENT
+#define MAX_SENSE_EVENT_PER_SECOND     16
        /*
         * filter of sense code uevent
         * setting bit X (0x00 - 0x0e) of sense_event_filter enables
         * uevent for sense key X
         */
-       unsigned long           sense_event_filter;
+       unsigned long   sense_event_filter;
+       /*
+        * To rate limit uevents to MAX_SENSE_EVENT_PER_SECOND, we track
+        * nano second time of MAX_SENSE_EVENT_PER_SECOND most recent
+        * events. If there are already MAX_SENSE_EVENT_PER_SECOND in the
+        * past seconds, new event is dropped.
+        */
+       u64             latest_event_times[MAX_SENSE_EVENT_PER_SECOND];
+       int             latest_event_idx;
+       spinlock_t      latest_event_lock;
 #endif
 
        struct device           sdev_gendev,
-- 
2.9.3