Provide SMP safe locking for all_mddevs list.
the all_mddevs_lock is added to protect all_mddevs and mddev_map.
ITERATE_MDDEV is moved to md.c (it isn't needed elsewhere) and enhanced
to take the lock appropriately and always have a refcount on the object
that is given to the body of the loop.
mddev_find is changed so that the structure is allocated outside a lock,
but test-and-set is done inside the lock.
----------- Diffstat output ------------
./drivers/md/md.c | 73 +++++++++++++++++++++++++++++++++-----------
./include/linux/raid/md_k.h | 10 ------
2 files changed, 55 insertions(+), 28 deletions(-)
--- ./drivers/md/md.c 2002/06/18 05:33:38 1.19
+++ ./drivers/md/md.c 2002/06/18 06:05:22 1.20
@@ -127,8 +127,33 @@
/*
* Enables to iterate over all existing md arrays
+ * all_mddevs_lock protects this list as well as mddev_map.
*/
static LIST_HEAD(all_mddevs);
+static spinlock_t all_mddevs_lock = SPIN_LOCK_UNLOCKED;
+
+
+/*
+ * iterates through all used mddevs in the system.
+ * We take care to grab the all_mddevs_lock whenever navigating
+ * the list, and to always hold a refcount when unlocked.
+ * Any code which breaks out of this loop while own
+ * a reference to the current mddev and must mddev_put it.
+ */
+#define ITERATE_MDDEV(mddev,tmp) \
+ \
+ for (spin_lock(&all_mddevs_lock), \
+ (tmp = all_mddevs.next), \
+ (mddev = NULL); \
+ (void)(tmp != &all_mddevs && \
+ mddev_get(list_entry(tmp, mddev_t, all_mddevs))),\
+ spin_unlock(&all_mddevs_lock), \
+ (mddev ? mddev_put(mddev):(void)NULL), \
+ (mddev = list_entry(tmp, mddev_t, all_mddevs)), \
+ (tmp != &all_mddevs); \
+ spin_lock(&all_mddevs_lock), \
+ (tmp = tmp->next) \
+ )
static mddev_t *mddev_map[MAX_MD_DEVS];
@@ -146,7 +171,7 @@
static void mddev_put(mddev_t *mddev)
{
- if (!atomic_dec_and_test(&mddev->active))
+ if (!atomic_dec_and_lock(&mddev->active, &all_mddevs_lock))
return;
if (!mddev->sb && list_empty(&mddev->disks)) {
list_del(&mddev->all_mddevs);
@@ -154,33 +179,44 @@
kfree(mddev);
MOD_DEC_USE_COUNT;
}
+ spin_unlock(&all_mddevs_lock);
}
static mddev_t * mddev_find(int unit)
{
- mddev_t *mddev;
+ mddev_t *mddev, *new = NULL;
- if ((mddev = mddev_map[unit])) {
- return mddev_get(mddev);
+ retry:
+ spin_lock(&all_mddevs_lock);
+ if (mddev_map[unit]) {
+ mddev = mddev_get(mddev_map[unit]);
+ spin_unlock(&all_mddevs_lock);
+ if (new)
+ kfree(new);
+ return mddev;
+ }
+ if (new) {
+ mddev_map[unit] = new;
+ list_add(&new->all_mddevs, &all_mddevs);
+ spin_unlock(&all_mddevs_lock);
+ MOD_INC_USE_COUNT;
+ return new;
}
- mddev = (mddev_t *) kmalloc(sizeof(*mddev), GFP_KERNEL);
- if (!mddev)
- return NULL;
-
- memset(mddev, 0, sizeof(*mddev));
+ spin_unlock(&all_mddevs_lock);
- mddev->__minor = unit;
- init_MUTEX(&mddev->reconfig_sem);
- INIT_LIST_HEAD(&mddev->disks);
- INIT_LIST_HEAD(&mddev->all_mddevs);
- atomic_set(&mddev->active, 1);
+ new = (mddev_t *) kmalloc(sizeof(*new), GFP_KERNEL);
+ if (!new)
+ return NULL;
- mddev_map[unit] = mddev;
- list_add(&mddev->all_mddevs, &all_mddevs);
+ memset(new, 0, sizeof(*new));
- MOD_INC_USE_COUNT;
+ new->__minor = unit;
+ init_MUTEX(&new->reconfig_sem);
+ INIT_LIST_HEAD(&new->disks);
+ INIT_LIST_HEAD(&new->all_mddevs);
+ atomic_set(&new->active, 1);
- return mddev;
+ goto retry;
}
static inline int mddev_lock(mddev_t * mddev)
@@ -3192,6 +3228,7 @@
mddev2->curr_resync < 2)) {
flush_curr_signals();
err = -EINTR;
+ mddev_put(mddev2);
goto out;
}
}
--- ./include/linux/raid/md_k.h 2002/06/18 05:29:05 1.8
+++ ./include/linux/raid/md_k.h 2002/06/18 06:05:22 1.9
@@ -277,16 +277,6 @@
#define ITERATE_RDEV_PENDING(rdev,tmp) \
ITERATE_RDEV_GENERIC(pending_raid_disks,pending,rdev,tmp)
-/*
- * iterates through all used mddevs in the system.
- */
-#define ITERATE_MDDEV(mddev,tmp) \
- \
- for (tmp = all_mddevs.next; \
- mddev = list_entry(tmp, mddev_t, all_mddevs), \
- tmp = tmp->next, tmp->prev != &all_mddevs \
- ; )
-
#define xchg_values(x,y) do { __typeof__(x) __tmp = x; \
x = y; y = __tmp; } while (0)
-
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