1 files changed, 57 insertions, 0 deletions

diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index ae0aaa9d42fa..4f440b3e89fe 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -97,7 +97,13 @@ struct partition_meta_info {
 
 struct hd_struct {
         sector_t start_sect;
+        /*
+         * nr_sects is protected by sequence counter. One might extend a
+         * partition while IO is happening to it and update of nr_sects
+         * can be non-atomic on 32bit machines with 64bit sector_t.
+         */
         sector_t nr_sects;
+        seqcount_t nr_sects_seq;
         sector_t alignment_offset;
         unsigned int discard_alignment;
         struct device __dev;
@@ -647,6 +653,57 @@ static inline void hd_struct_put(struct hd_struct *part)
                 __delete_partition(part);
 }
 
+/*
+ * Any access of part->nr_sects which is not protected by partition
+ * bd_mutex or gendisk bdev bd_mutex, should be done using this
+ * accessor function.
+ *
+ * Code written along the lines of i_size_read() and i_size_write().
+ * CONFIG_PREEMPT case optimizes the case of UP kernel with preemption
+ * on.
+ */
+static inline sector_t part_nr_sects_read(struct hd_struct *part)
+{
+#if BITS_PER_LONG==32 && defined(CONFIG_LBDAF) && defined(CONFIG_SMP)
+        sector_t nr_sects;
+        unsigned seq;
+        do {
+                seq = read_seqcount_begin(&part->nr_sects_seq);
+                nr_sects = part->nr_sects;
+        } while (read_seqcount_retry(&part->nr_sects_seq, seq));
+        return nr_sects;
+#elif BITS_PER_LONG==32 && defined(CONFIG_LBDAF) && defined(CONFIG_PREEMPT)
+        sector_t nr_sects;
+
+        preempt_disable();
+        nr_sects = part->nr_sects;
+        preempt_enable();
+        return nr_sects;
+#else
+        return part->nr_sects;
+#endif
+}
+
+/*
+ * Should be called with mutex lock held (typically bd_mutex) of partition
+ * to provide mutual exlusion among writers otherwise seqcount might be
+ * left in wrong state leaving the readers spinning infinitely.
+ */
+static inline void part_nr_sects_write(struct hd_struct *part, sector_t size)
+{
+#if BITS_PER_LONG==32 && defined(CONFIG_LBDAF) && defined(CONFIG_SMP)
+        write_seqcount_begin(&part->nr_sects_seq);
+        part->nr_sects = size;
+        write_seqcount_end(&part->nr_sects_seq);
+#elif BITS_PER_LONG==32 && defined(CONFIG_LBDAF) && defined(CONFIG_PREEMPT)
+        preempt_disable();
+        part->nr_sects = size;
+        preempt_enable();
+#else
+        part->nr_sects = size;
+#endif
+}
+
 #else /* CONFIG_BLOCK */
 
 static inline void printk_all_partitions(void) { }