Commit 2ca3310e authored by Alasdair G Kergon's avatar Alasdair G Kergon Committed by Linus Torvalds

[PATCH] device-mapper: fix md->lock deadlocks in core

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: default avatarAlasdair G Kergon <agk@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 4e90188b
......@@ -55,10 +55,10 @@ union map_info *dm_get_mapinfo(struct bio *bio)
*/
#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 inline void free_tio(struct mapped_device *md, struct target_io *tio)
*/
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 @@ static int dm_request(request_queue_t *q, struct bio *bio)
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 @@ static int dm_request(request_queue_t *q, struct bio *bio)
* 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 @@ static struct mapped_device *alloc_dev(unsigned int minor, int persistent)
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 @@ static int __bind(struct mapped_device *md, struct dm_table *t)
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 dm_swap_table(struct mapped_device *md, struct dm_table *table)
{
int r = -EINVAL;
down_write(&md->lock);
down(&md->suspend_lock);
/* device must be suspended */
if (!dm_suspended(md))
......@@ -973,7 +975,7 @@ int dm_swap_table(struct mapped_device *md, struct dm_table *table)
r = __bind(md, table);
out:
up_write(&md->lock);
up(&md->suspend_lock);
return r;
}
......@@ -981,16 +983,13 @@ int dm_swap_table(struct mapped_device *md, struct dm_table *table)
* 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 @@ static int __lock_fs(struct mapped_device *md)
/* 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 @@ static int __lock_fs(struct mapped_device *md)
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 @@ static void __unlock_fs(struct mapped_device *md)
*/
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 @@ int dm_suspend(struct mapped_device *md)
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 @@ int dm_suspend(struct mapped_device *md)
}
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 @@ int dm_resume(struct mapped_device *md)
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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