[PATCH] dm: fix idr minor allocation

One part of the system can attempt to use a mapped device before another has
finished initialising it or while it is being freed.

This patch introduces a place holder value, MINOR_ALLOCED, to mark the minor
as allocated but in a state where it can't be used, such as mid-allocation or
mid-free.  At the end of the initialization, it replaces the place holder with
the pointer to the mapped_device, making it available to the rest of the dm
subsystem.

[akpm: too late for 2.6.17 - suitable for 2.6.17.x after it has settled]

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 16 insertions, 3 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 4d710b7a133b..87d8ca1121e2 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -54,6 +54,8 @@ union map_info *dm_get_mapinfo(struct bio *bio)
         return NULL;
 }
 
+#define MINOR_ALLOCED ((void *)-1)
+
 /*
  * Bits for the md->flags field.
  */
@@ -777,7 +779,7 @@ static int specific_minor(struct mapped_device *md, unsigned int minor)
                 goto out;
         }
 
-        r = idr_get_new_above(&_minor_idr, md, minor, &m);
+        r = idr_get_new_above(&_minor_idr, MINOR_ALLOCED, minor, &m);
         if (r) {
                 goto out;
         }
@@ -806,7 +808,7 @@ static int next_free_minor(struct mapped_device *md, unsigned int *minor)
                 goto out;
         }
 
-        r = idr_get_new(&_minor_idr, md, &m);
+        r = idr_get_new(&_minor_idr, MINOR_ALLOCED, &m);
         if (r) {
                 goto out;
         }
@@ -833,6 +835,7 @@ static struct mapped_device *alloc_dev(unsigned int minor, int persistent)
 {
         int r;
         struct mapped_device *md = kmalloc(sizeof(*md), GFP_KERNEL);
+        void *old_md;
 
         if (!md) {
                 DMWARN("unable to allocate device, out of memory.");
@@ -888,6 +891,13 @@ static struct mapped_device *alloc_dev(unsigned int minor, int persistent)
         init_waitqueue_head(&md->wait);
         init_waitqueue_head(&md->eventq);
 
+        /* Populate the mapping, nobody knows we exist yet */
+        mutex_lock(&_minor_lock);
+        old_md = idr_replace(&_minor_idr, md, minor);
+        mutex_unlock(&_minor_lock);
+
+        BUG_ON(old_md != MINOR_ALLOCED);
+
         return md;
 
  bad4:
@@ -1018,7 +1028,7 @@ static struct mapped_device *dm_find_md(dev_t dev)
         mutex_lock(&_minor_lock);
 
         md = idr_find(&_minor_idr, minor);
-        if (!md || (dm_disk(md)->first_minor != minor))
+        if (md && (md == MINOR_ALLOCED || (dm_disk(md)->first_minor != minor)))
                 md = NULL;
 
         mutex_unlock(&_minor_lock);
@@ -1057,6 +1067,9 @@ void dm_put(struct mapped_device *md)
 
         if (atomic_dec_and_test(&md->holders)) {
                 map = dm_get_table(md);
+                mutex_lock(&_minor_lock);
+                idr_replace(&_minor_idr, MINOR_ALLOCED, dm_disk(md)->first_minor);
+                mutex_unlock(&_minor_lock);
                 if (!dm_suspended(md)) {
                         dm_table_presuspend_targets(map);
                         dm_table_postsuspend_targets(map);