[2.6.22 PATCH 02/26] dm raid1: one kmirrord per mirror

From: Alasdair G Kergon
Date: Tue May 08 2007 - 15:43:24 EST

From: Holger Smolinski <smolinski@xxxxxxxxxx>

This patch replaces the single instance of kmirrord by one instance per
mirror set. This change is required to avoid a deadlock in kmirrord when
the persistent dirty log of a mirror itself resides on a mirror. The single
instance of kmirrord then issues a sync write to the dirty log in
write_bits which gets deferred to kmirrord itself later in the call chain.
But kmirrord never does the deferred work because it is still waiting for
the sync write_bits.

_mirror_sets is removed as it no longer needed, and we always flush the
workqueue before destroying it to ensure all work is complete before
destroying it.

Signed-off-by: Holger Smolinski <smolinski@xxxxxxxxxx>
Signed-off-by: Alasdair G Kergon <agk@xxxxxxxxxx>
---

drivers/md/dm-raid1.c | 81 ++++++++++++++++----------------------------------
1 files changed, 27 insertions(+), 54 deletions(-)

Index: linux-2.6.21/drivers/md/dm-raid1.c
===================================================================
--- linux-2.6.21.orig/drivers/md/dm-raid1.c 2007-05-01 17:38:32.000000000 +0100
+++ linux-2.6.21/drivers/md/dm-raid1.c 2007-05-01 17:40:46.000000000 +0100
@@ -22,15 +22,8 @@

#define DM_MSG_PREFIX "raid1"

-static struct workqueue_struct *_kmirrord_wq;
-static struct work_struct _kmirrord_work;
static DECLARE_WAIT_QUEUE_HEAD(_kmirrord_recovery_stopped);

-static inline void wake(void)
-{
- queue_work(_kmirrord_wq, &_kmirrord_work);
-}
-
/*-----------------------------------------------------------------
* Region hash
*
@@ -136,6 +129,9 @@ struct mirror_set {

struct mirror *default_mirror; /* Default mirror */

+ struct workqueue_struct *kmirrord_wq;
+ struct work_struct kmirrord_work;
+
unsigned int nr_mirrors;
struct mirror mirror[0];
};
@@ -153,6 +149,11 @@ static inline sector_t region_to_sector(
return region << rh->region_shift;
}

+static void wake(struct mirror_set *ms)
+{
+ queue_work(ms->kmirrord_wq, &ms->kmirrord_work);
+}
+
/* FIXME move this */
static void queue_bio(struct mirror_set *ms, struct bio *bio, int rw);

@@ -471,7 +472,7 @@ static void rh_dec(struct region_hash *r
spin_unlock_irqrestore(&rh->region_lock, flags);

if (should_wake)
- wake();
+ wake(rh->ms);
}

/*
@@ -558,7 +559,7 @@ static void rh_recovery_end(struct regio
list_add(&reg->list, &reg->rh->recovered_regions);
spin_unlock_irq(&rh->region_lock);

- wake();
+ wake(rh->ms);
}

static void rh_flush(struct region_hash *rh)
@@ -592,7 +593,7 @@ static void rh_start_recovery(struct reg
for (i = 0; i < MAX_RECOVERY; i++)
up(&rh->recovery_count);

- wake();
+ wake(rh->ms);
}

/*
@@ -870,11 +871,10 @@ static void do_writes(struct mirror_set
/*-----------------------------------------------------------------
* kmirrord
*---------------------------------------------------------------*/
-static LIST_HEAD(_mirror_sets);
-static DECLARE_RWSEM(_mirror_sets_lock);
-
-static void do_mirror(struct mirror_set *ms)
+static void do_mirror(struct work_struct *work)
{
+ struct mirror_set *ms =container_of(work, struct mirror_set,
+ kmirrord_work);
struct bio_list reads, writes;

spin_lock(&ms->lock);
@@ -890,16 +890,6 @@ static void do_mirror(struct mirror_set
do_writes(ms, &writes);
}

-static void do_work(struct work_struct *ignored)
-{
- struct mirror_set *ms;
-
- down_read(&_mirror_sets_lock);
- list_for_each_entry (ms, &_mirror_sets, list)
- do_mirror(ms);
- up_read(&_mirror_sets_lock);
-}
-
/*-----------------------------------------------------------------
* Target functions
*---------------------------------------------------------------*/
@@ -978,23 +968,6 @@ static int get_mirror(struct mirror_set
return 0;
}

-static int add_mirror_set(struct mirror_set *ms)
-{
- down_write(&_mirror_sets_lock);
- list_add_tail(&ms->list, &_mirror_sets);
- up_write(&_mirror_sets_lock);
- wake();
-
- return 0;
-}
-
-static void del_mirror_set(struct mirror_set *ms)
-{
- down_write(&_mirror_sets_lock);
- list_del(&ms->list);
- up_write(&_mirror_sets_lock);
-}
-
/*
* Create dirty log: log_type #log_params <log_params>
*/
@@ -1096,13 +1069,22 @@ static int mirror_ctr(struct dm_target *
ti->private = ms;
ti->split_io = ms->rh.region_size;

+ ms->kmirrord_wq = create_singlethread_workqueue("kmirrord");
+ if (!ms->kmirrord_wq) {
+ DMERR("couldn't start kmirrord");
+ free_context(ms, ti, m);
+ return -ENOMEM;
+ }
+ INIT_WORK(&ms->kmirrord_work, do_mirror);
+
r = kcopyd_client_create(DM_IO_PAGES, &ms->kcopyd_client);
if (r) {
+ destroy_workqueue(ms->kmirrord_wq);
free_context(ms, ti, ms->nr_mirrors);
return r;
}

- add_mirror_set(ms);
+ wake(ms);
return 0;
}

@@ -1110,8 +1092,9 @@ static void mirror_dtr(struct dm_target
{
struct mirror_set *ms = (struct mirror_set *) ti->private;

- del_mirror_set(ms);
+ flush_workqueue(ms->kmirrord_wq);
kcopyd_client_destroy(ms->kcopyd_client);
+ destroy_workqueue(ms->kmirrord_wq);
free_context(ms, ti, ms->nr_mirrors);
}

@@ -1127,7 +1110,7 @@ static void queue_bio(struct mirror_set
spin_unlock(&ms->lock);

if (should_wake)
- wake();
+ wake(ms);
}

/*
@@ -1270,20 +1253,11 @@ static int __init dm_mirror_init(void)
if (r)
return r;

- _kmirrord_wq = create_singlethread_workqueue("kmirrord");
- if (!_kmirrord_wq) {
- DMERR("couldn't start kmirrord");
- dm_dirty_log_exit();
- return r;
- }
- INIT_WORK(&_kmirrord_work, do_work);
-
r = dm_register_target(&mirror_target);
if (r < 0) {
DMERR("%s: Failed to register mirror target",
mirror_target.name);
dm_dirty_log_exit();
- destroy_workqueue(_kmirrord_wq);
}

return r;
@@ -1297,7 +1271,6 @@ static void __exit dm_mirror_exit(void)
if (r < 0)
DMERR("%s: unregister failed %d", mirror_target.name, r);

- destroy_workqueue(_kmirrord_wq);
dm_dirty_log_exit();
}

-
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