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dm: rework queueing and suspension

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Rework shutting down on suspend and document the associated rules.

Drop write lock in __split_and_process_bio to allow more processing
concurrency.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mikulas Patocka 2009-04-09 00:27:15 +01:00 committed by Alasdair G Kergon
parent 54d9a1b451
commit 3b00b2036f
1 changed files with 32 additions and 8 deletions
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40
drivers/md/dm.c
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@ -1434,18 +1434,21 @@ static void dm_wq_work(struct work_struct *work)
down_write(&md->io_lock);
while (1) {
while (!test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) {
spin_lock_irq(&md->deferred_lock);
c = bio_list_pop(&md->deferred);
spin_unlock_irq(&md->deferred_lock);
if (!c) {
clear_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
clear_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags);
break;
}
up_write(&md->io_lock);
__split_and_process_bio(md, c);
down_write(&md->io_lock);
}
up_write(&md->io_lock);
@ -1453,8 +1456,9 @@ static void dm_wq_work(struct work_struct *work)
static void dm_queue_flush(struct mapped_device *md)
{
clear_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
smp_mb__after_clear_bit();
queue_work(md->wq, &md->work);
flush_workqueue(md->wq);
}
/*
@ -1572,22 +1576,36 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
}
/*
* First we set the DMF_QUEUE_IO_TO_THREAD flag so no more ios
* will be mapped.
* Here we must make sure that no processes are submitting requests
* to target drivers i.e. no one may be executing
* __split_and_process_bio. This is called from dm_request and
* dm_wq_work.
*
* To get all processes out of __split_and_process_bio in dm_request,
* we take the write lock. To prevent any process from reentering
* __split_and_process_bio from dm_request, we set
* DMF_QUEUE_IO_TO_THREAD.
*
* To quiesce the thread (dm_wq_work), we set DMF_BLOCK_IO_FOR_SUSPEND
* and call flush_workqueue(md->wq). flush_workqueue will wait until
* dm_wq_work exits and DMF_BLOCK_IO_FOR_SUSPEND will prevent any
* further calls to __split_and_process_bio from dm_wq_work.
*/
down_write(&md->io_lock);
set_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
set_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags);
up_write(&md->io_lock);
flush_workqueue(md->wq);
/*
* Wait for the already-mapped ios to complete.
* At this point no more requests are entering target request routines.
* We call dm_wait_for_completion to wait for all existing requests
* to finish.
*/
r = dm_wait_for_completion(md, TASK_INTERRUPTIBLE);
down_write(&md->io_lock);
if (noflush)
clear_bit(DMF_NOFLUSH_SUSPENDING, &md->flags);
up_write(&md->io_lock);
@ -1600,6 +1618,12 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
goto out; /* pushback list is already flushed, so skip flush */
}
/*
* If dm_wait_for_completion returned 0, the device is completely
* quiescent now. There is no request-processing activity. All new
* requests are being added to md->deferred list.
*/
dm_table_postsuspend_targets(map);
set_bit(DMF_SUSPENDED, &md->flags);