Merge branch 'for-3.8/drivers' of git://git.kernel.dk/linux-block

Pull block driver update from Jens Axboe:
 "Now that the core bits are in, here are the driver bits for 3.8.  The
  branch contains:

   - A huge pile of drbd bits that were dumped from the 3.7 merge
     window.  Following that, it was both made perfectly clear that
     there is going to be no more over-the-wall pulls and how the
     situation on individual pulls can be improved.

   - A few cleanups from Akinobu Mita for drbd and cciss.

   - Queue improvement for loop from Lukas.  This grew into adding a
     generic interface for waiting/checking an even with a specific
     lock, allowing this to be pulled out of md and now loop and drbd is
     also using it.

   - A few fixes for xen back/front block driver from Roger Pau Monne.

   - Partition improvements from Stephen Warren, allowing partiion UUID
     to be used as an identifier."

* 'for-3.8/drivers' of git://git.kernel.dk/linux-block: (609 commits)
  drbd: update Kconfig to match current dependencies
  drbd: Fix drbdsetup wait-connect, wait-sync etc... commands
  drbd: close race between drbd_set_role and drbd_connect
  drbd: respect no-md-barriers setting also when changed online via disk-options
  drbd: Remove obsolete check
  drbd: fixup after wait_even_lock_irq() addition to generic code
  loop: Limit the number of requests in the bio list
  wait: add wait_event_lock_irq() interface
  xen-blkfront: free allocated page
  xen-blkback: move free persistent grants code
  block: partition: msdos: provide UUIDs for partitions
  init: reduce PARTUUID min length to 1 from 36
  block: store partition_meta_info.uuid as a string
  cciss: use check_signature()
  cciss: cleanup bitops usage
  drbd: use copy_highpage
  drbd: if the replication link breaks during handshake, keep retrying
  drbd: check return of kmalloc in receive_uuids
  drbd: Broadcast sync progress no more often than once per second
  drbd: don't try to clear bits once the disk has failed
  ...

1 files changed, 225 insertions, 134 deletions

diff --git a/lib/lru_cache.c b/lib/lru_cache.c
index a07e7268d7ed..d71d89498943 100644
--- a/lib/lru_cache.c
+++ b/lib/lru_cache.c
@@ -44,8 +44,8 @@ MODULE_LICENSE("GPL");
 } while (0)
 
 #define RETURN(x...)     do { \
-        clear_bit(__LC_PARANOIA, &lc->flags); \
-        smp_mb__after_clear_bit(); return x ; } while (0)
+        clear_bit_unlock(__LC_PARANOIA, &lc->flags); \
+        return x ; } while (0)
 
 /* BUG() if e is not one of the elements tracked by lc */
 #define PARANOIA_LC_ELEMENT(lc, e) do { \
@@ -55,9 +55,40 @@ MODULE_LICENSE("GPL");
         BUG_ON(i >= lc_->nr_elements);  \
         BUG_ON(lc_->lc_element[i] != e_); } while (0)
 
+
+/* We need to atomically
+ *  - try to grab the lock (set LC_LOCKED)
+ *  - only if there is no pending transaction
+ *    (neither LC_DIRTY nor LC_STARVING is set)
+ * Because of PARANOIA_ENTRY() above abusing lc->flags as well,
+ * it is not sufficient to just say
+ *      return 0 == cmpxchg(&lc->flags, 0, LC_LOCKED);
+ */
+int lc_try_lock(struct lru_cache *lc)
+{
+        unsigned long val;
+        do {
+                val = cmpxchg(&lc->flags, 0, LC_LOCKED);
+        } while (unlikely (val == LC_PARANOIA));
+        /* Spin until no-one is inside a PARANOIA_ENTRY()/RETURN() section. */
+        return 0 == val;
+#if 0
+        /* Alternative approach, spin in case someone enters or leaves a
+         * PARANOIA_ENTRY()/RETURN() section. */
+        unsigned long old, new, val;
+        do {
+                old = lc->flags & LC_PARANOIA;
+                new = old | LC_LOCKED;
+                val = cmpxchg(&lc->flags, old, new);
+        } while (unlikely (val == (old ^ LC_PARANOIA)));
+        return old == val;
+#endif
+}
+
 /**
  * lc_create - prepares to track objects in an active set
  * @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
+ * @max_pending_changes: maximum changes to accumulate until a transaction is required
  * @e_count: number of elements allowed to be active simultaneously
  * @e_size: size of the tracked objects
  * @e_off: offset to the &struct lc_element member in a tracked object
@@ -66,6 +97,7 @@ MODULE_LICENSE("GPL");
  * or NULL on (allocation) failure.
  */
 struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
+                unsigned max_pending_changes,
                 unsigned e_count, size_t e_size, size_t e_off)
 {
         struct hlist_head *slot = NULL;
@@ -98,12 +130,13 @@ struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
         INIT_LIST_HEAD(&lc->in_use);
         INIT_LIST_HEAD(&lc->lru);
         INIT_LIST_HEAD(&lc->free);
+        INIT_LIST_HEAD(&lc->to_be_changed);
 
         lc->name = name;
         lc->element_size = e_size;
         lc->element_off = e_off;
         lc->nr_elements = e_count;
-        lc->new_number = LC_FREE;
+        lc->max_pending_changes = max_pending_changes;
         lc->lc_cache = cache;
         lc->lc_element = element;
         lc->lc_slot = slot;
@@ -117,6 +150,7 @@ struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
                 e = p + e_off;
                 e->lc_index = i;
                 e->lc_number = LC_FREE;
+                e->lc_new_number = LC_FREE;
                 list_add(&e->list, &lc->free);
                 element[i] = e;
         }
@@ -175,15 +209,15 @@ void lc_reset(struct lru_cache *lc)
         INIT_LIST_HEAD(&lc->in_use);
         INIT_LIST_HEAD(&lc->lru);
         INIT_LIST_HEAD(&lc->free);
+        INIT_LIST_HEAD(&lc->to_be_changed);
         lc->used = 0;
         lc->hits = 0;
         lc->misses = 0;
         lc->starving = 0;
-        lc->dirty = 0;
+        lc->locked = 0;
         lc->changed = 0;
+        lc->pending_changes = 0;
         lc->flags = 0;
-        lc->changing_element = NULL;
-        lc->new_number = LC_FREE;
         memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);
 
         for (i = 0; i < lc->nr_elements; i++) {
@@ -194,6 +228,7 @@ void lc_reset(struct lru_cache *lc)
                 /* re-init it */
                 e->lc_index = i;
                 e->lc_number = LC_FREE;
+                e->lc_new_number = LC_FREE;
                 list_add(&e->list, &lc->free);
         }
 }
@@ -208,14 +243,14 @@ size_t lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc)
         /* NOTE:
          * total calls to lc_get are
          * (starving + hits + misses)
-         * misses include "dirty" count (update from an other thread in
+         * misses include "locked" count (update from an other thread in
          * progress) and "changed", when this in fact lead to an successful
          * update of the cache.
          */
         return seq_printf(seq, "\t%s: used:%u/%u "
-                "hits:%lu misses:%lu starving:%lu dirty:%lu changed:%lu\n",
+                "hits:%lu misses:%lu starving:%lu locked:%lu changed:%lu\n",
                 lc->name, lc->used, lc->nr_elements,
-                lc->hits, lc->misses, lc->starving, lc->dirty, lc->changed);
+                lc->hits, lc->misses, lc->starving, lc->locked, lc->changed);
 }
 
 static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr)
@@ -224,16 +259,8 @@ static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr)
 }
 
 
-/**
- * lc_find - find element by label, if present in the hash table
- * @lc: The lru_cache object
- * @enr: element number
- *
- * Returns the pointer to an element, if the element with the requested
- * "label" or element number is present in the hash table,
- * or NULL if not found. Does not change the refcnt.
- */
-struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
+static struct lc_element *__lc_find(struct lru_cache *lc, unsigned int enr,
+                bool include_changing)
 {
         struct hlist_node *n;
         struct lc_element *e;
@@ -241,29 +268,48 @@ struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
         BUG_ON(!lc);
         BUG_ON(!lc->nr_elements);
         hlist_for_each_entry(e, n, lc_hash_slot(lc, enr), colision) {
-                if (e->lc_number == enr)
+                /* "about to be changed" elements, pending transaction commit,
+                 * are hashed by their "new number". "Normal" elements have
+                 * lc_number == lc_new_number. */
+                if (e->lc_new_number != enr)
+                        continue;
+                if (e->lc_new_number == e->lc_number || include_changing)
                         return e;
+                break;
         }
         return NULL;
 }
 
-/* returned element will be "recycled" immediately */
-static struct lc_element *lc_evict(struct lru_cache *lc)
+/**
+ * lc_find - find element by label, if present in the hash table
+ * @lc: The lru_cache object
+ * @enr: element number
+ *
+ * Returns the pointer to an element, if the element with the requested
+ * "label" or element number is present in the hash table,
+ * or NULL if not found. Does not change the refcnt.
+ * Ignores elements that are "about to be used", i.e. not yet in the active
+ * set, but still pending transaction commit.
+ */
+struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
 {
-        struct list_head  *n;
-        struct lc_element *e;
-
-        if (list_empty(&lc->lru))
-                return NULL;
-
-        n = lc->lru.prev;
-        e = list_entry(n, struct lc_element, list);
-
-        PARANOIA_LC_ELEMENT(lc, e);
+        return __lc_find(lc, enr, 0);
+}
 
-        list_del(&e->list);
-        hlist_del(&e->colision);
-        return e;
+/**
+ * lc_is_used - find element by label
+ * @lc: The lru_cache object
+ * @enr: element number
+ *
+ * Returns true, if the element with the requested "label" or element number is
+ * present in the hash table, and is used (refcnt > 0).
+ * Also finds elements that are not _currently_ used but only "about to be
+ * used", i.e. on the "to_be_changed" list, pending transaction commit.
+ */
+bool lc_is_used(struct lru_cache *lc, unsigned int enr)
+{
+        struct lc_element *e = __lc_find(lc, enr, 1);
+        return e && e->refcnt;
 }
 
 /**
@@ -280,22 +326,34 @@ void lc_del(struct lru_cache *lc, struct lc_element *e)
         PARANOIA_LC_ELEMENT(lc, e);
         BUG_ON(e->refcnt);
 
-        e->lc_number = LC_FREE;
+        e->lc_number = e->lc_new_number = LC_FREE;
         hlist_del_init(&e->colision);
         list_move(&e->list, &lc->free);
         RETURN();
 }
 
-static struct lc_element *lc_get_unused_element(struct lru_cache *lc)
+static struct lc_element *lc_prepare_for_change(struct lru_cache *lc, unsigned new_number)
 {
         struct list_head *n;
+        struct lc_element *e;
+
+        if (!list_empty(&lc->free))
+                n = lc->free.next;
+        else if (!list_empty(&lc->lru))
+                n = lc->lru.prev;
+        else
+                return NULL;
+
+        e = list_entry(n, struct lc_element, list);
+        PARANOIA_LC_ELEMENT(lc, e);
 
-        if (list_empty(&lc->free))
-                return lc_evict(lc);
+        e->lc_new_number = new_number;
+        if (!hlist_unhashed(&e->colision))
+                __hlist_del(&e->colision);
+        hlist_add_head(&e->colision, lc_hash_slot(lc, new_number));
+        list_move(&e->list, &lc->to_be_changed);
 
-        n = lc->free.next;
-        list_del(n);
-        return list_entry(n, struct lc_element, list);
+        return e;
 }
 
 static int lc_unused_element_available(struct lru_cache *lc)
@@ -308,45 +366,7 @@ static int lc_unused_element_available(struct lru_cache *lc)
         return 0;
 }
 
-
-/**
- * lc_get - get element by label, maybe change the active set
- * @lc: the lru cache to operate on
- * @enr: the label to look up
- *
- * Finds an element in the cache, increases its usage count,
- * "touches" and returns it.
- *
- * In case the requested number is not present, it needs to be added to the
- * cache. Therefore it is possible that an other element becomes evicted from
- * the cache. In either case, the user is notified so he is able to e.g. keep
- * a persistent log of the cache changes, and therefore the objects in use.
- *
- * Return values:
- *  NULL
- *     The cache was marked %LC_STARVING,
- *     or the requested label was not in the active set
- *     and a changing transaction is still pending (@lc was marked %LC_DIRTY).
- *     Or no unused or free element could be recycled (@lc will be marked as
- *     %LC_STARVING, blocking further lc_get() operations).
- *
- *  pointer to the element with the REQUESTED element number.
- *     In this case, it can be used right away
- *
- *  pointer to an UNUSED element with some different element number,
- *          where that different number may also be %LC_FREE.
- *
- *          In this case, the cache is marked %LC_DIRTY (blocking further changes),
- *          and the returned element pointer is removed from the lru list and
- *          hash collision chains.  The user now should do whatever housekeeping
- *          is necessary.
- *          Then he must call lc_changed(lc,element_pointer), to finish
- *          the change.
- *
- * NOTE: The user needs to check the lc_number on EACH use, so he recognizes
- *       any cache set change.
- */
-struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
+static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, bool may_change)
 {
         struct lc_element *e;
 
@@ -356,8 +376,12 @@ struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
                 RETURN(NULL);
         }
 
-        e = lc_find(lc, enr);
-        if (e) {
+        e = __lc_find(lc, enr, 1);
+        /* if lc_new_number != lc_number,
+         * this enr is currently being pulled in already,
+         * and will be available once the pending transaction
+         * has been committed. */
+        if (e && e->lc_new_number == e->lc_number) {
                 ++lc->hits;
                 if (e->refcnt++ == 0)
                         lc->used++;
@@ -366,6 +390,26 @@ struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
         }
 
         ++lc->misses;
+        if (!may_change)
+                RETURN(NULL);
+
+        /* It has been found above, but on the "to_be_changed" list, not yet
+         * committed.  Don't pull it in twice, wait for the transaction, then
+         * try again */
+        if (e)
+                RETURN(NULL);
+
+        /* To avoid races with lc_try_lock(), first, mark us dirty
+         * (using test_and_set_bit, as it implies memory barriers), ... */
+        test_and_set_bit(__LC_DIRTY, &lc->flags);
+
+        /* ... only then check if it is locked anyways. If lc_unlock clears
+         * the dirty bit again, that's not a problem, we will come here again.
+         */
+        if (test_bit(__LC_LOCKED, &lc->flags)) {
+                ++lc->locked;
+                RETURN(NULL);
+        }
 
         /* In case there is nothing available and we can not kick out
          * the LRU element, we have to wait ...
@@ -375,71 +419,109 @@ struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
                 RETURN(NULL);
         }
 
-        /* it was not present in the active set.
-         * we are going to recycle an unused (or even "free") element.
-         * user may need to commit a transaction to record that change.
-         * we serialize on flags & TF_DIRTY */
-        if (test_and_set_bit(__LC_DIRTY, &lc->flags)) {
-                ++lc->dirty;
+        /* It was not present in the active set.  We are going to recycle an
+         * unused (or even "free") element, but we won't accumulate more than
+         * max_pending_changes changes.  */
+        if (lc->pending_changes >= lc->max_pending_changes)
                 RETURN(NULL);
-        }
 
-        e = lc_get_unused_element(lc);
+        e = lc_prepare_for_change(lc, enr);
         BUG_ON(!e);
 
         clear_bit(__LC_STARVING, &lc->flags);
         BUG_ON(++e->refcnt != 1);
         lc->used++;
-
-        lc->changing_element = e;
-        lc->new_number = enr;
+        lc->pending_changes++;
 
         RETURN(e);
 }
 
-/* similar to lc_get,
- * but only gets a new reference on an existing element.
- * you either get the requested element, or NULL.
- * will be consolidated into one function.
+/**
+ * lc_get - get element by label, maybe change the active set
+ * @lc: the lru cache to operate on
+ * @enr: the label to look up
+ *
+ * Finds an element in the cache, increases its usage count,
+ * "touches" and returns it.
+ *
+ * In case the requested number is not present, it needs to be added to the
+ * cache. Therefore it is possible that an other element becomes evicted from
+ * the cache. In either case, the user is notified so he is able to e.g. keep
+ * a persistent log of the cache changes, and therefore the objects in use.
+ *
+ * Return values:
+ *  NULL
+ *     The cache was marked %LC_STARVING,
+ *     or the requested label was not in the active set
+ *     and a changing transaction is still pending (@lc was marked %LC_DIRTY).
+ *     Or no unused or free element could be recycled (@lc will be marked as
+ *     %LC_STARVING, blocking further lc_get() operations).
+ *
+ *  pointer to the element with the REQUESTED element number.
+ *     In this case, it can be used right away
+ *
+ *  pointer to an UNUSED element with some different element number,
+ *          where that different number may also be %LC_FREE.
+ *
+ *          In this case, the cache is marked %LC_DIRTY,
+ *          so lc_try_lock() will no longer succeed.
+ *          The returned element pointer is moved to the "to_be_changed" list,
+ *          and registered with the new element number on the hash collision chains,
+ *          so it is possible to pick it up from lc_is_used().
+ *          Up to "max_pending_changes" (see lc_create()) can be accumulated.
+ *          The user now should do whatever housekeeping is necessary,
+ *          typically serialize on lc_try_lock_for_transaction(), then call
+ *          lc_committed(lc) and lc_unlock(), to finish the change.
+ *
+ * NOTE: The user needs to check the lc_number on EACH use, so he recognizes
+ *       any cache set change.
  */
-struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
+struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
 {
-        struct lc_element *e;
-
-        PARANOIA_ENTRY();
-        if (lc->flags & LC_STARVING) {
-                ++lc->starving;
-                RETURN(NULL);
-        }
+        return __lc_get(lc, enr, 1);
+}
 
-        e = lc_find(lc, enr);
-        if (e) {
-                ++lc->hits;
-                if (e->refcnt++ == 0)
-                        lc->used++;
-                list_move(&e->list, &lc->in_use); /* Not evictable... */
-        }
-        RETURN(e);
+/**
+ * lc_try_get - get element by label, if present; do not change the active set
+ * @lc: the lru cache to operate on
+ * @enr: the label to look up
+ *
+ * Finds an element in the cache, increases its usage count,
+ * "touches" and returns it.
+ *
+ * Return values:
+ *  NULL
+ *     The cache was marked %LC_STARVING,
+ *     or the requested label was not in the active set
+ *
+ *  pointer to the element with the REQUESTED element number.
+ *     In this case, it can be used right away
+ */
+struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
+{
+        return __lc_get(lc, enr, 0);
 }
 
 /**
- * lc_changed - tell @lc that the change has been recorded
+ * lc_committed - tell @lc that pending changes have been recorded
  * @lc: the lru cache to operate on
- * @e: the element pending label change
+ *
+ * User is expected to serialize on explicit lc_try_lock_for_transaction()
+ * before the transaction is started, and later needs to lc_unlock() explicitly
+ * as well.
  */
-void lc_changed(struct lru_cache *lc, struct lc_element *e)
+void lc_committed(struct lru_cache *lc)
 {
+        struct lc_element *e, *tmp;
+
         PARANOIA_ENTRY();
-        BUG_ON(e != lc->changing_element);
-        PARANOIA_LC_ELEMENT(lc, e);
-        ++lc->changed;
-        e->lc_number = lc->new_number;
-        list_add(&e->list, &lc->in_use);
-        hlist_add_head(&e->colision, lc_hash_slot(lc, lc->new_number));
-        lc->changing_element = NULL;
-        lc->new_number = LC_FREE;
-        clear_bit(__LC_DIRTY, &lc->flags);
-        smp_mb__after_clear_bit();
+        list_for_each_entry_safe(e, tmp, &lc->to_be_changed, list) {
+                /* count number of changes, not number of transactions */
+                ++lc->changed;
+                e->lc_number = e->lc_new_number;
+                list_move(&e->list, &lc->in_use);
+        }
+        lc->pending_changes = 0;
         RETURN();
 }
 
@@ -458,13 +540,12 @@ unsigned int lc_put(struct lru_cache *lc, struct lc_element *e)
         PARANOIA_ENTRY();
         PARANOIA_LC_ELEMENT(lc, e);
         BUG_ON(e->refcnt == 0);
-        BUG_ON(e == lc->changing_element);
+        BUG_ON(e->lc_number != e->lc_new_number);
         if (--e->refcnt == 0) {
                 /* move it to the front of LRU. */
                 list_move(&e->list, &lc->lru);
                 lc->used--;
-                clear_bit(__LC_STARVING, &lc->flags);
-                smp_mb__after_clear_bit();
+                clear_bit_unlock(__LC_STARVING, &lc->flags);
         }
         RETURN(e->refcnt);
 }
@@ -504,16 +585,24 @@ unsigned int lc_index_of(struct lru_cache *lc, struct lc_element *e)
 void lc_set(struct lru_cache *lc, unsigned int enr, int index)
 {
         struct lc_element *e;
+        struct list_head *lh;
 
         if (index < 0 || index >= lc->nr_elements)
                 return;
 
         e = lc_element_by_index(lc, index);
-        e->lc_number = enr;
+        BUG_ON(e->lc_number != e->lc_new_number);
+        BUG_ON(e->refcnt != 0);
 
+        e->lc_number = e->lc_new_number = enr;
         hlist_del_init(&e->colision);
-        hlist_add_head(&e->colision, lc_hash_slot(lc, enr));
-        list_move(&e->list, e->refcnt ? &lc->in_use : &lc->lru);
+        if (enr == LC_FREE)
+                lh = &lc->free;
+        else {
+                hlist_add_head(&e->colision, lc_hash_slot(lc, enr));
+                lh = &lc->lru;
+        }
+        list_move(&e->list, lh);
 }
 
 /**
@@ -553,8 +642,10 @@ EXPORT_SYMBOL(lc_try_get);
 EXPORT_SYMBOL(lc_find);
 EXPORT_SYMBOL(lc_get);
 EXPORT_SYMBOL(lc_put);
-EXPORT_SYMBOL(lc_changed);
+EXPORT_SYMBOL(lc_committed);
 EXPORT_SYMBOL(lc_element_by_index);
 EXPORT_SYMBOL(lc_index_of);
 EXPORT_SYMBOL(lc_seq_printf_stats);
 EXPORT_SYMBOL(lc_seq_dump_details);
+EXPORT_SYMBOL(lc_try_lock);
+EXPORT_SYMBOL(lc_is_used);