drbd: Replaced md_io_mutex by an atomic: md_io_in_use

The new function drbd_md_get_buffer() aborts waiting for the buffer
in case the disk failes in the meantime.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

4 files changed, 51 insertions, 19 deletions

diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
index c64ca6b956cf..4271352dd72b 100644
--- a/drivers/block/drbd/drbd_actlog.c
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -65,6 +65,23 @@ struct drbd_atodb_wait {
 
 int w_al_write_transaction(struct drbd_conf *, struct drbd_work *, int);
 
+void *drbd_md_get_buffer(struct drbd_conf *mdev)
+{
+        int r;
+
+        wait_event(mdev->misc_wait,
+                   (r = atomic_cmpxchg(&mdev->md_io_in_use, 0, 1)) == 0 ||
+                   mdev->state.disk <= D_FAILED);
+
+        return r ? NULL : page_address(mdev->md_io_page);
+}
+
+void drbd_md_put_buffer(struct drbd_conf *mdev)
+{
+        if (atomic_dec_and_test(&mdev->md_io_in_use))
+                wake_up(&mdev->misc_wait);
+}
+
 static int _drbd_md_sync_page_io(struct drbd_conf *mdev,
                                  struct drbd_backing_dev *bdev,
                                  struct page *page, sector_t sector,
@@ -90,6 +107,7 @@ static int _drbd_md_sync_page_io(struct drbd_conf *mdev,
         bio->bi_end_io = drbd_md_io_complete;
         bio->bi_rw = rw;
 
+        atomic_inc(&mdev->md_io_in_use); /* drbd_md_put_buffer() is in the completion handler */
         if (drbd_insert_fault(mdev, (rw & WRITE) ? DRBD_FAULT_MD_WR : DRBD_FAULT_MD_RD))
                 bio_endio(bio, -EIO);
         else
@@ -109,7 +127,7 @@ int drbd_md_sync_page_io(struct drbd_conf *mdev, struct drbd_backing_dev *bdev,
         int offset = 0;
         struct page *iop = mdev->md_io_page;
 
-        D_ASSERT(mutex_is_locked(&mdev->md_io_mutex));
+        D_ASSERT(atomic_read(&mdev->md_io_in_use) == 1);
 
         BUG_ON(!bdev->md_bdev);
 
@@ -326,8 +344,13 @@ w_al_write_transaction(struct drbd_conf *mdev, struct drbd_work *w, int unused)
                 return 1;
         }
 
-        mutex_lock(&mdev->md_io_mutex); /* protects md_io_buffer, al_tr_cycle, ... */
-        buffer = (struct al_transaction *)page_address(mdev->md_io_page);
+        buffer = drbd_md_get_buffer(mdev); /* protects md_io_buffer, al_tr_cycle, ... */
+        if (!buffer) {
+                dev_err(DEV, "disk failed while waiting for md_io buffer\n");
+                complete(&((struct update_al_work *)w)->event);
+                put_ldev(mdev);
+                return 1;
+        }
 
         buffer->magic = __constant_cpu_to_be32(DRBD_MAGIC);
         buffer->tr_number = cpu_to_be32(mdev->al_tr_number);
@@ -372,7 +395,7 @@ w_al_write_transaction(struct drbd_conf *mdev, struct drbd_work *w, int unused)
         D_ASSERT(mdev->al_tr_pos < MD_AL_MAX_SIZE);
         mdev->al_tr_number++;
 
-        mutex_unlock(&mdev->md_io_mutex);
+        drbd_md_put_buffer(mdev);
 
         complete(&((struct update_al_work *)w)->event);
         put_ldev(mdev);
@@ -441,8 +464,9 @@ int drbd_al_read_log(struct drbd_conf *mdev, struct drbd_backing_dev *bdev)
         /* lock out all other meta data io for now,
          * and make sure the page is mapped.
          */
-        mutex_lock(&mdev->md_io_mutex);
-        buffer = page_address(mdev->md_io_page);
+        buffer = drbd_md_get_buffer(mdev);
+        if (!buffer)
+                return 0;
 
         /* Find the valid transaction in the log */
         for (i = 0; i <= mx; i++) {
@@ -450,7 +474,7 @@ int drbd_al_read_log(struct drbd_conf *mdev, struct drbd_backing_dev *bdev)
                 if (rv == 0)
                         continue;
                 if (rv == -1) {
-                        mutex_unlock(&mdev->md_io_mutex);
+                        drbd_md_put_buffer(mdev);
                         return 0;
                 }
                 cnr = be32_to_cpu(buffer->tr_number);
@@ -476,7 +500,7 @@ int drbd_al_read_log(struct drbd_conf *mdev, struct drbd_backing_dev *bdev)
 
         if (!found_valid) {
                 dev_warn(DEV, "No usable activity log found.\n");
-                mutex_unlock(&mdev->md_io_mutex);
+                drbd_md_put_buffer(mdev);
                 return 1;
         }
 
@@ -491,7 +515,7 @@ int drbd_al_read_log(struct drbd_conf *mdev, struct drbd_backing_dev *bdev)
                 rv = drbd_al_read_tr(mdev, bdev, buffer, i);
                 ERR_IF(rv == 0) goto cancel;
                 if (rv == -1) {
-                        mutex_unlock(&mdev->md_io_mutex);
+                        drbd_md_put_buffer(mdev);
                         return 0;
                 }
 
@@ -532,7 +556,7 @@ cancel:
                 mdev->al_tr_pos = 0;
 
         /* ok, we are done with it */
-        mutex_unlock(&mdev->md_io_mutex);
+        drbd_md_put_buffer(mdev);
 
         dev_info(DEV, "Found %d transactions (%d active extents) in activity log.\n",
              transactions, active_extents);
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index 91e69ffd5566..55cae74911e8 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -1095,7 +1095,7 @@ struct drbd_conf {
         struct page *md_io_page;        /* one page buffer for md_io */
         struct page *md_io_tmpp;        /* for logical_block_size != 512 */
         struct drbd_md_io md_io;
-        struct mutex md_io_mutex;       /* protects the md_io, md_io_page and md_io_tmpp */
+        atomic_t md_io_in_use;          /* protects the md_io, md_io_page and md_io_tmpp */
         spinlock_t al_lock;
         wait_queue_head_t al_wait;
         struct lru_cache *act_log;      /* activity log */
@@ -1537,8 +1537,10 @@ extern void resume_next_sg(struct drbd_conf *mdev);
 extern void suspend_other_sg(struct drbd_conf *mdev);
 extern int drbd_resync_finished(struct drbd_conf *mdev);
 /* maybe rather drbd_main.c ? */
+extern void *drbd_md_get_buffer(struct drbd_conf *mdev);
+extern void drbd_md_put_buffer(struct drbd_conf *mdev);
 extern int drbd_md_sync_page_io(struct drbd_conf *mdev,
-                struct drbd_backing_dev *bdev, sector_t sector, int rw);
+                                struct drbd_backing_dev *bdev, sector_t sector, int rw);
 extern void drbd_ov_oos_found(struct drbd_conf*, sector_t, int);
 extern void drbd_rs_controller_reset(struct drbd_conf *mdev);
 
diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 16969c2b96cd..1b59ab3ab9c7 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -3043,8 +3043,8 @@ void drbd_init_set_defaults(struct drbd_conf *mdev)
         atomic_set(&mdev->rs_sect_in, 0);
         atomic_set(&mdev->rs_sect_ev, 0);
         atomic_set(&mdev->ap_in_flight, 0);
+        atomic_set(&mdev->md_io_in_use, 0);
 
-        mutex_init(&mdev->md_io_mutex);
         mutex_init(&mdev->data.mutex);
         mutex_init(&mdev->meta.mutex);
         sema_init(&mdev->data.work.s, 0);
@@ -3722,8 +3722,10 @@ void drbd_md_sync(struct drbd_conf *mdev)
         if (!get_ldev_if_state(mdev, D_FAILED))
                 return;
 
-        mutex_lock(&mdev->md_io_mutex);
-        buffer = (struct meta_data_on_disk *)page_address(mdev->md_io_page);
+        buffer = drbd_md_get_buffer(mdev);
+        if (!buffer)
+                goto out;
+
         memset(buffer, 0, 512);
 
         buffer->la_size = cpu_to_be64(drbd_get_capacity(mdev->this_bdev));
@@ -3754,7 +3756,8 @@ void drbd_md_sync(struct drbd_conf *mdev)
          * since we updated it on metadata. */
         mdev->ldev->md.la_size_sect = drbd_get_capacity(mdev->this_bdev);
 
-        mutex_unlock(&mdev->md_io_mutex);
+        drbd_md_put_buffer(mdev);
+out:
         put_ldev(mdev);
 }
 
@@ -3774,8 +3777,9 @@ int drbd_md_read(struct drbd_conf *mdev, struct drbd_backing_dev *bdev)
         if (!get_ldev_if_state(mdev, D_ATTACHING))
                 return ERR_IO_MD_DISK;
 
-        mutex_lock(&mdev->md_io_mutex);
-        buffer = (struct meta_data_on_disk *)page_address(mdev->md_io_page);
+        buffer = drbd_md_get_buffer(mdev);
+        if (!buffer)
+                goto out;
 
         if (!drbd_md_sync_page_io(mdev, bdev, bdev->md.md_offset, READ)) {
                 /* NOTE: can't do normal error processing here as this is
@@ -3836,7 +3840,8 @@ int drbd_md_read(struct drbd_conf *mdev, struct drbd_backing_dev *bdev)
                 mdev->sync_conf.al_extents = 127;
 
  err:
-        mutex_unlock(&mdev->md_io_mutex);
+        drbd_md_put_buffer(mdev);
+ out:
         put_ldev(mdev);
 
         return rv;
diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index eedfe311c403..94a128b49f4f 100644
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -78,6 +78,7 @@ void drbd_md_io_complete(struct bio *bio, int error)
         md_io->error = error;
 
         complete(&md_io->event);
+        drbd_md_put_buffer(mdev);
 }
 
 /* reads on behalf of the partner,