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Subject[42/91] dm ioctl: release _hash_lock between devices in remove_all
2.6.34-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>

commit 98f332855effef02aeb738e4d62e9a5b903c52fd upstream.

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>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/md/dm-ioctl.c | 44 +++++++++++++++++++++++++-------------------
1 file changed, 25 insertions(+), 19 deletions(-)
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -249,40 +249,46 @@ static void __hash_remove(struct hash_ce

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 int dm_hash_rename(uint32_t cookie, uint32_t *flags, const char *old,



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