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Fix zvol partition creation during module load 

Partitions for a zvol device were not appearing in /dev/zvol/<pool>/
at module load time for a couple of reasons.

1) The Linux block layer expects a block device to have a non-zero
   capacity during add_disk().  If the capacity is zero it does not
   attempt to open the device which means we never trigger a partition
   scan.  The device capacity was just being set during the first open.

2) Because we expect to be adding a block device to the zvol_state_list
   during zvol_create_minor() the zvol_state_lock() is held.  This
   can result in a deadlock in add_disk() when it attempts to open
   the block device via zvol_open() which also takes this same lock.
   To avoid this issue special handling has been added to zvol_open()
   and zvol_release() to allow the mutex owner to enter these functions
   without retaking the lock.

3) In __zvol_create_minor() the call to dmu_objset_disown() must occur
   before the call to add_disk().  As mentioned above add_disk() results
   in a call to zvol_open() which will attempt to call dmu_objset_own()
   again on the objset.  If the objset is already open it will fail
   resulting in a failed open.  This in turn means the kernel will be
   unable to read the partition information from the device.
This commit is contained in:
Brian Behlendorf 2010-08-04 14:39:12 -07:00
parent a54f5dddf1
commit f3aa3b93df
1 changed files with 36 additions and 9 deletions
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45
module/zfs/zvol.c
View File

@ -815,9 +815,19 @@ static int
zvol_open(struct block_device *bdev, fmode_t flag)
{
zvol_state_t *zv = bdev->bd_disk->private_data;
int error = 0;
int error = 0, drop_mutex = 0;
/*
* If the caller is already holding the mutex do not take it
* again, this will happen as part of zvol_create_minor().
* Once add_disk() is called the device is live and the kernel
* will attempt to open it to read the partition information.
*/
if (!mutex_owned(&zvol_state_lock)) {
mutex_enter(&zvol_state_lock);
drop_mutex = 1;
}
mutex_enter(&zvol_state_lock);
ASSERT3P(zv, !=, NULL);
if (zv->zv_open_count == 0) {
@ -839,7 +849,8 @@ out_open_count:
zvol_last_close(zv);
out_mutex:
mutex_exit(&zvol_state_lock);
if (drop_mutex)
mutex_exit(&zvol_state_lock);
check_disk_change(bdev);
@ -850,15 +861,21 @@ static int
zvol_release(struct gendisk *disk, fmode_t mode)
{
zvol_state_t *zv = disk->private_data;
int drop_mutex = 0;
if (!mutex_owned(&zvol_state_lock)) {
mutex_enter(&zvol_state_lock);
drop_mutex = 1;
}
mutex_enter(&zvol_state_lock);
ASSERT3P(zv, !=, NULL);
ASSERT3U(zv->zv_open_count, >, 0);
zv->zv_open_count--;
if (zv->zv_open_count == 0)
zvol_last_close(zv);
mutex_exit(&zvol_state_lock);
if (drop_mutex)
mutex_exit(&zvol_state_lock);
return (0);
}
@ -1083,6 +1100,7 @@ __zvol_create_minor(const char *name)
zvol_state_t *zv;
objset_t *os;
dmu_object_info_t *doi;
uint64_t volsize;
unsigned minor = 0;
int error = 0;
@ -1104,6 +1122,10 @@ __zvol_create_minor(const char *name)
if (error)
goto out_dmu_objset_disown;
error = zap_lookup(os, ZVOL_ZAP_OBJ, "size", 8, 1, &volsize);
if (error)
goto out_dmu_objset_disown;
error = zvol_find_minor(&minor);
if (error)
goto out_dmu_objset_disown;
@ -1118,23 +1140,28 @@ __zvol_create_minor(const char *name)
zv->zv_flags |= ZVOL_RDONLY;
zv->zv_volblocksize = doi->doi_data_block_size;
zv->zv_volsize = volsize;
zv->zv_objset = os;
set_capacity(zv->zv_disk, zv->zv_volsize >> 9);
if (zil_replay_disable)
zil_destroy(dmu_objset_zil(os), B_FALSE);
else
zil_replay(os, zv, zvol_replay_vector);
zvol_insert(zv);
add_disk(zv->zv_disk);
error = 0;
out_dmu_objset_disown:
dmu_objset_disown(os, zvol_tag);
zv->zv_objset = NULL;
out_doi:
kmem_free(doi, sizeof(dmu_object_info_t));
out:
if (error == 0) {
zvol_insert(zv);
add_disk(zv->zv_disk);
}
return (error);
}