This patch is an attempt to fix deadlocks discovered in the core dm.
The problems boil down to md->lock having to be held in too many
places, so I've split it into two: md->suspend_lock and md->io_lock.
suspend_lock is now held throughout dm_suspended() as well as
dm_resume() and dm_swap_table() so that these functions cannot
run concurrently: there's no requirement for that and it added
complexity.
DMF_FS_LOCKED becomes redundant: DMF_SUSPENDED provides adequate
protection.
Signed-Off-By: Alasdair G Kergon <[email protected]>
--- diff/drivers/md/dm.c 2005-07-11 22:57:58.000000000 +0100
+++ source/drivers/md/dm.c 2005-07-11 23:03:21.000000000 +0100
@@ -55,10 +55,10 @@
*/
#define DMF_BLOCK_IO 0
#define DMF_SUSPENDED 1
-#define DMF_FS_LOCKED 2
struct mapped_device {
- struct rw_semaphore lock;
+ struct rw_semaphore io_lock;
+ struct semaphore suspend_lock;
rwlock_t map_lock;
atomic_t holders;
@@ -248,16 +248,16 @@
*/
static int queue_io(struct mapped_device *md, struct bio *bio)
{
- down_write(&md->lock);
+ down_write(&md->io_lock);
if (!test_bit(DMF_BLOCK_IO, &md->flags)) {
- up_write(&md->lock);
+ up_write(&md->io_lock);
return 1;
}
bio_list_add(&md->deferred, bio);
- up_write(&md->lock);
+ up_write(&md->io_lock);
return 0; /* deferred successfully */
}
@@ -568,14 +568,14 @@
int r;
struct mapped_device *md = q->queuedata;
- down_read(&md->lock);
+ down_read(&md->io_lock);
/*
* If we're suspended we have to queue
* this io for later.
*/
while (test_bit(DMF_BLOCK_IO, &md->flags)) {
- up_read(&md->lock);
+ up_read(&md->io_lock);
if (bio_rw(bio) == READA) {
bio_io_error(bio, bio->bi_size);
@@ -594,11 +594,11 @@
* We're in a while loop, because someone could suspend
* before we get to the following read lock.
*/
- down_read(&md->lock);
+ down_read(&md->io_lock);
}
__split_bio(md, bio);
- up_read(&md->lock);
+ up_read(&md->io_lock);
return 0;
}
@@ -747,7 +747,8 @@
goto bad1;
memset(md, 0, sizeof(*md));
- init_rwsem(&md->lock);
+ init_rwsem(&md->io_lock);
+ init_MUTEX(&md->suspend_lock);
rwlock_init(&md->map_lock);
atomic_set(&md->holders, 1);
atomic_set(&md->event_nr, 0);
@@ -844,13 +845,14 @@
if (size == 0)
return 0;
+ dm_table_get(t);
+ dm_table_event_callback(t, event_callback, md);
+
write_lock(&md->map_lock);
md->map = t;
+ dm_table_set_restrictions(t, q);
write_unlock(&md->map_lock);
- dm_table_get(t);
- dm_table_event_callback(t, event_callback, md);
- dm_table_set_restrictions(t, q);
return 0;
}
@@ -963,7 +965,7 @@
{
int r = -EINVAL;
- down_write(&md->lock);
+ down(&md->suspend_lock);
/* device must be suspended */
if (!dm_suspended(md))
@@ -973,7 +975,7 @@
r = __bind(md, table);
out:
- up_write(&md->lock);
+ up(&md->suspend_lock);
return r;
}
@@ -981,16 +983,13 @@
* Functions to lock and unlock any filesystem running on the
* device.
*/
-static int __lock_fs(struct mapped_device *md)
+static int lock_fs(struct mapped_device *md)
{
int r = -ENOMEM;
- if (test_and_set_bit(DMF_FS_LOCKED, &md->flags))
- return 0;
-
md->frozen_bdev = bdget_disk(md->disk, 0);
if (!md->frozen_bdev) {
- DMWARN("bdget failed in __lock_fs");
+ DMWARN("bdget failed in lock_fs");
goto out;
}
@@ -1004,7 +1003,7 @@
/* don't bdput right now, we don't want the bdev
* to go away while it is locked. We'll bdput
- * in __unlock_fs
+ * in unlock_fs
*/
return 0;
@@ -1013,15 +1012,11 @@
md->frozen_sb = NULL;
md->frozen_bdev = NULL;
out:
- clear_bit(DMF_FS_LOCKED, &md->flags);
return r;
}
-static void __unlock_fs(struct mapped_device *md)
+static void unlock_fs(struct mapped_device *md)
{
- if (!test_and_clear_bit(DMF_FS_LOCKED, &md->flags))
- return;
-
thaw_bdev(md->frozen_bdev, md->frozen_sb);
bdput(md->frozen_bdev);
@@ -1038,13 +1033,14 @@
*/
int dm_suspend(struct mapped_device *md)
{
- struct dm_table *map;
+ struct dm_table *map = NULL;
DECLARE_WAITQUEUE(wait, current);
int r = -EINVAL;
- down_read(&md->lock);
- if (test_bit(DMF_BLOCK_IO, &md->flags))
- goto out_read_unlock;
+ down(&md->suspend_lock);
+
+ if (dm_suspended(md))
+ goto out;
map = dm_get_table(md);
@@ -1052,36 +1048,22 @@
dm_table_presuspend_targets(map);
/* Flush I/O to the device. */
- r = __lock_fs(md);
- if (r) {
- dm_table_put(map);
- goto out_read_unlock;
- }
-
- up_read(&md->lock);
+ r = lock_fs(md);
+ if (r)
+ goto out;
/*
* First we set the BLOCK_IO flag so no more ios will be mapped.
- *
- * If the flag is already set we know another thread is trying to
- * suspend as well, so we leave the fs locked for this thread.
*/
- r = -EINVAL;
- down_write(&md->lock);
- if (test_and_set_bit(DMF_BLOCK_IO, &md->flags)) {
- if (map)
- dm_table_put(map);
- goto out_write_unlock;
- }
+ down_write(&md->io_lock);
+ set_bit(DMF_BLOCK_IO, &md->flags);
add_wait_queue(&md->wait, &wait);
- up_write(&md->lock);
+ up_write(&md->io_lock);
/* unplug */
- if (map) {
+ if (map)
dm_table_unplug_all(map);
- dm_table_put(map);
- }
/*
* Then we wait for the already mapped ios to
@@ -1097,32 +1079,28 @@
}
set_current_state(TASK_RUNNING);
- down_write(&md->lock);
+ down_write(&md->io_lock);
remove_wait_queue(&md->wait, &wait);
/* were we interrupted ? */
r = -EINTR;
- if (atomic_read(&md->pending))
- goto out_unfreeze;
-
- set_bit(DMF_SUSPENDED, &md->flags);
+ if (atomic_read(&md->pending)) {
+ up_write(&md->io_lock);
+ unlock_fs(md);
+ clear_bit(DMF_BLOCK_IO, &md->flags);
+ goto out;
+ }
+ up_write(&md->io_lock);
- map = dm_get_table(md);
dm_table_postsuspend_targets(map);
- dm_table_put(map);
- up_write(&md->lock);
- return 0;
+ set_bit(DMF_SUSPENDED, &md->flags);
-out_unfreeze:
- __unlock_fs(md);
- clear_bit(DMF_BLOCK_IO, &md->flags);
-out_write_unlock:
- up_write(&md->lock);
- return r;
+ r = 0;
-out_read_unlock:
- up_read(&md->lock);
+out:
+ dm_table_put(map);
+ up(&md->suspend_lock);
return r;
}
@@ -1132,31 +1110,35 @@
struct bio *def;
struct dm_table *map = NULL;
- down_write(&md->lock);
- if (!dm_suspended(md)) {
- up_write(&md->lock);
+ down(&md->suspend_lock);
+ if (!dm_suspended(md))
goto out;
- }
map = dm_get_table(md);
- if (!map || !dm_table_get_size(map)) {
- up_write(&md->lock);
+ if (!map || !dm_table_get_size(map))
goto out;
- }
dm_table_resume_targets(map);
- clear_bit(DMF_SUSPENDED, &md->flags);
+
+ down_write(&md->io_lock);
clear_bit(DMF_BLOCK_IO, &md->flags);
def = bio_list_get(&md->deferred);
__flush_deferred_io(md, def);
- up_write(&md->lock);
- __unlock_fs(md);
+ up_write(&md->io_lock);
+
+ unlock_fs(md);
+
+ clear_bit(DMF_SUSPENDED, &md->flags);
+
dm_table_unplug_all(map);
r = 0;
+
out:
dm_table_put(map);
+ up(&md->suspend_lock);
+
return r;
}
-
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