1 files changed, 26 insertions, 15 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 56ad4531b412..381b09bb562b 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -355,6 +355,12 @@ throtl_start_new_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
                         tg->slice_end[rw], jiffies);
 }
 
+static inline void throtl_set_slice_end(struct throtl_data *td,
+                struct throtl_grp *tg, bool rw, unsigned long jiffy_end)
+{
+        tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
+}
+
 static inline void throtl_extend_slice(struct throtl_data *td,
                 struct throtl_grp *tg, bool rw, unsigned long jiffy_end)
 {
@@ -391,6 +397,16 @@ throtl_trim_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
         if (throtl_slice_used(td, tg, rw))
                 return;
 
+        /*
+         * A bio has been dispatched. Also adjust slice_end. It might happen
+         * that initially cgroup limit was very low resulting in high
+         * slice_end, but later limit was bumped up and bio was dispached
+         * sooner, then we need to reduce slice_end. A high bogus slice_end
+         * is bad because it does not allow new slice to start.
+         */
+
+        throtl_set_slice_end(td, tg, rw, jiffies + throtl_slice);
+
         time_elapsed = jiffies - tg->slice_start[rw];
 
         nr_slices = time_elapsed / throtl_slice;
@@ -645,7 +661,7 @@ static int throtl_dispatch_tg(struct throtl_data *td, struct throtl_grp *tg,
 {
         unsigned int nr_reads = 0, nr_writes = 0;
         unsigned int max_nr_reads = throtl_grp_quantum*3/4;
-        unsigned int max_nr_writes = throtl_grp_quantum - nr_reads;
+        unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;
         struct bio *bio;
 
         /* Try to dispatch 75% READS and 25% WRITES */
@@ -709,26 +725,21 @@ static void throtl_process_limit_change(struct throtl_data *td)
         struct throtl_grp *tg;
         struct hlist_node *pos, *n;
 
-        /*
-         * Make sure atomic_inc() effects from
-         * throtl_update_blkio_group_read_bps(), group of functions are
-         * visible.
-         * Is this required or smp_mb__after_atomic_inc() was suffcient
-         * after the atomic_inc().
-         */
-        smp_rmb();
         if (!atomic_read(&td->limits_changed))
                 return;
 
         throtl_log(td, "limit changed =%d", atomic_read(&td->limits_changed));
 
-        hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
-                /*
-                 * Do I need an smp_rmb() here to make sure tg->limits_changed
-                 * update is visible. I am relying on smp_rmb() at the
-                 * beginning of function and not putting a new one here.
-                 */
+        /*
+         * Make sure updates from throtl_update_blkio_group_read_bps() group
+         * of functions to tg->limits_changed are visible. We do not
+         * want update td->limits_changed to be visible but update to
+         * tg->limits_changed not being visible yet on this cpu. Hence
+         * the read barrier.
+         */
+        smp_rmb();
 
+        hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
                 if (throtl_tg_on_rr(tg) && tg->limits_changed) {
                         throtl_log_tg(td, tg, "limit change rbps=%llu wbps=%llu"
                                 " riops=%u wiops=%u", tg->bps[READ],