dm ioctl: release _hash_lock between devices in remove_all

This patch changes dm_hash_remove_all() to release _hash_lock when
removing a device.  After removing the device, dm_hash_remove_all()
takes _hash_lock and searches the hash from scratch again.

This patch is a preparation for the next patch, which changes device
deletion code to wait for md reference to be 0.  Without this patch,
the wait in the next patch may cause AB-BA deadlock:
  CPU0                                CPU1
  -----------------------------------------------------------------------
  dm_hash_remove_all()
    down_write(_hash_lock)
                                      table_status()
                                        md = find_device()
                                               dm_get(md)
                                                 <increment md->holders>
                                        dm_get_live_or_inactive_table()
                                          dm_get_inactive_table()
                                            down_write(_hash_lock)
    <in the md deletion code>
      <wait for md->holders to be 0>

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: stable@kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 25 insertions, 19 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 79ee5ba217f2..6a6d475f8e80 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -249,40 +249,46 @@ static void __hash_remove(struct hash_cell *hc)
 
 static void dm_hash_remove_all(int keep_open_devices)
 {
-        int i, dev_skipped, dev_removed;
+        int i, dev_skipped;
         struct hash_cell *hc;
-        struct list_head *tmp, *n;
+        struct mapped_device *md;
+
+retry:
+        dev_skipped = 0;
 
         down_write(&_hash_lock);
 
-retry:
-        dev_skipped = dev_removed = 0;
         for (i = 0; i < NUM_BUCKETS; i++) {
-                list_for_each_safe (tmp, n, _name_buckets + i) {
-                        hc = list_entry(tmp, struct hash_cell, name_list);
+                list_for_each_entry(hc, _name_buckets + i, name_list) {
+                        md = hc->md;
+                        dm_get(md);
 
-                        if (keep_open_devices &&
-                            dm_lock_for_deletion(hc->md)) {
+                        if (keep_open_devices && dm_lock_for_deletion(md)) {
+                                dm_put(md);
                                 dev_skipped++;
                                 continue;
                         }
+
                         __hash_remove(hc);
-                        dev_removed = 1;
-                }
-        }
 
-        /*
-         * Some mapped devices may be using other mapped devices, so if any
-         * still exist, repeat until we make no further progress.
-         */
-        if (dev_skipped) {
-                if (dev_removed)
-                        goto retry;
+                        up_write(&_hash_lock);
 
-                DMWARN("remove_all left %d open device(s)", dev_skipped);
+                        dm_put(md);
+
+                        /*
+                         * Some mapped devices may be using other mapped
+                         * devices, so repeat until we make no further
+                         * progress.  If a new mapped device is created
+                         * here it will also get removed.
+                         */
+                        goto retry;
+                }
         }
 
         up_write(&_hash_lock);
+
+        if (dev_skipped)
+                DMWARN("remove_all left %d open device(s)", dev_skipped);
 }
 
 static struct mapped_device *dm_hash_rename(struct dm_ioctl *param,