The queue-congestion-dm-implementation patch in 2.6.4-rc1-mm1 (included below) allows a DM device to query the lower-level device(s) during the queue-congestion APIs. However, it must wait on an internal semaphore (md->lock) before passing the call down to the lower-level devices. The problem is that the higher-level caller is holding a spinlock at the same time. Here is one such stack-trace I have been seeing: Debug: sleeping function called from invalid context at include/linux/ rwsem.h:43 in_atomic():1, irqs_disabled():0 Call Trace: [<c012456b>] __might_sleep+0xab/0xd0 [<c03a0771>] dm_any_congested+0x21/0x60 [<c0192a82>] sync_sb_inodes+0x2d2/0x2f0 [<c0192b4c>] writeback_inodes+0xac/0x1d0 [<c014c68b>] wb_kupdate+0xdb/0x170 [<c014cf49>] __pdflush+0x1b9/0x380 [<c014d121>] pdflush+0x11/0x20 [<c014c5b0>] wb_kupdate+0x0/0x170 [<c013f6b6>] kthread+0xb6/0xc0 [<c014d110>] pdflush+0x0/0x20 [<c013f600>] kthread+0x0/0xc0 [<c01070cd>] kernel_thread_helper+0x5/0x18 I'm not sure how to fix this (or how serious a problem it is)...I'm just throwing this out there for discussion. -- Kevin Corry kevcorry@xxxxxxxxxx http://evms.sourceforge.net/ --- diff/drivers/md/dm-table.c 2004-03-01 14:36:06.000000000 +0000 +++ source/drivers/md/dm-table.c 2004-03-01 15:42:16.000000000 +0000 @@ -862,6 +862,20 @@ void dm_table_resume_targets(struct dm_t } } +int dm_table_any_congested(struct dm_table *t, int bdi_bits) +{ + struct list_head *d, *devices; + int r = 0; + + devices = dm_table_get_devices(t); + for (d = devices->next; d != devices; d = d->next) { + struct dm_dev *dd = list_entry(d, struct dm_dev, list); + request_queue_t *q = bdev_get_queue(dd->bdev); + r |= bdi_congested(&q->backing_dev_info, bdi_bits); + } + + return r; +} EXPORT_SYMBOL(dm_vcalloc); EXPORT_SYMBOL(dm_get_device); --- diff/drivers/md/dm.c 2004-03-01 14:36:06.000000000 +0000 +++ source/drivers/md/dm.c 2004-03-01 15:42:16.000000000 +0000 @@ -489,6 +489,18 @@ static int dm_request(request_queue_t *q return 0; } +static int dm_any_congested(void *congested_data, int bdi_bits) +{ + int r; + struct mapped_device *md = congested_data; + + down_read(&md->lock); + r = dm_table_any_congested(md->map, bdi_bits); + up_read(&md->lock); + + return r; +} + /*----------------------------------------------------------------- * A bitset is used to keep track of allocated minor numbers. *---------------------------------------------------------------*/ @@ -567,6 +579,8 @@ static struct mapped_device *alloc_dev(u goto bad1; md->queue->queuedata = md; + md->queue->backing_dev_info.congested_fn = dm_any_congested; + md->queue->backing_dev_info.congested_data = md; blk_queue_make_request(md->queue, dm_request); md->io_pool = mempool_create(MIN_IOS, mempool_alloc_slab, --- diff/drivers/md/dm.h 2004-03-01 14:36:06.000000000 +0000 +++ source/drivers/md/dm.h 2004-03-01 15:42:16.000000000 +0000 @@ -115,6 +115,7 @@ struct list_head *dm_table_get_devices(s int dm_table_get_mode(struct dm_table *t); void dm_table_suspend_targets(struct dm_table *t); void dm_table_resume_targets(struct dm_table *t); +int dm_table_any_congested(struct dm_table *t, int bdi_bits); /*----------------------------------------------------------------- * A registry of target types.