From: Milan Broz <mbroz@xxxxxxxxxx>
Process persistent exception store metadata IOs in a separate thread.
A snapshot may become invalid while inside generic_make_request().
A synchronous write is then needed to update the metadata while still
inside that function. Since the introduction of
md-dm-reduce-stack-usage-with-stacked-block-devices.patch this has to
be performed by a separate thread to avoid deadlock.
Signed-off-by: Milan Broz <mbroz@xxxxxxxxxx>
Signed-off-by: Alasdair G Kergon <agk@xxxxxxxxxx>
---
drivers/md/dm-exception-store.c | 48 +++++++++++++++++++++++++++++++++++-----
1 files changed, 43 insertions(+), 5 deletions(-)
Index: linux/drivers/md/dm-exception-store.c
===================================================================
--- linux.orig/drivers/md/dm-exception-store.c 2007-07-11 21:37:38.000000000 +0100
+++ linux/drivers/md/dm-exception-store.c 2007-07-11 21:37:44.000000000 +0100
@@ -125,6 +125,8 @@ struct pstore {
uint32_t callback_count;
struct commit_callback *callbacks;
struct dm_io_client *io_client;
+
+ struct workqueue_struct *metadata_wq;
};
static unsigned sectors_to_pages(unsigned sectors)
@@ -156,10 +158,24 @@ static void free_area(struct pstore *ps)
ps->area = NULL;
}
+struct mdata_req {
+ struct io_region *where;
+ struct dm_io_request *io_req;
+ struct work_struct work;
+ int result;
+};
+
+static void do_metadata(struct work_struct *work)
+{
+ struct mdata_req *req = container_of(work, struct mdata_req, work);
+
+ req->result = dm_io(req->io_req, 1, req->where, NULL);
+}
+
/*
* Read or write a chunk aligned and sized block of data from a device.
*/
-static int chunk_io(struct pstore *ps, uint32_t chunk, int rw)
+static int chunk_io(struct pstore *ps, uint32_t chunk, int rw, int metadata)
{
struct io_region where = {
.bdev = ps->snap->cow->bdev,
@@ -173,8 +189,23 @@ static int chunk_io(struct pstore *ps, u
.client = ps->io_client,
.notify.fn = NULL,
};
+ struct mdata_req req;
+
+ if (!metadata)
+ return dm_io(&io_req, 1, &where, NULL);
- return dm_io(&io_req, 1, &where, NULL);
+ req.where = &where;
+ req.io_req = &io_req;
+
+ /*
+ * Issue the synchronous I/O from a different thread
+ * to avoid generic_make_request recursion.
+ */
+ INIT_WORK(&req.work, do_metadata);
+ queue_work(ps->metadata_wq, &req.work);
+ flush_workqueue(ps->metadata_wq);
+
+ return req.result;
}
/*
@@ -189,7 +220,7 @@ static int area_io(struct pstore *ps, ui
/* convert a metadata area index to a chunk index */
chunk = 1 + ((ps->exceptions_per_area + 1) * area);
- r = chunk_io(ps, chunk, rw);
+ r = chunk_io(ps, chunk, rw, 0);
if (r)
return r;
@@ -230,7 +261,7 @@ static int read_header(struct pstore *ps
if (r)
return r;
- r = chunk_io(ps, 0, READ);
+ r = chunk_io(ps, 0, READ, 1);
if (r)
goto bad;
@@ -292,7 +323,7 @@ static int write_header(struct pstore *p
dh->version = cpu_to_le32(ps->version);
dh->chunk_size = cpu_to_le32(ps->snap->chunk_size);
- return chunk_io(ps, 0, WRITE);
+ return chunk_io(ps, 0, WRITE, 1);
}
/*
@@ -409,6 +440,7 @@ static void persistent_destroy(struct ex
{
struct pstore *ps = get_info(store);
+ destroy_workqueue(ps->metadata_wq);
dm_io_client_destroy(ps->io_client);
vfree(ps->callbacks);
free_area(ps);
@@ -588,6 +620,12 @@ int dm_create_persistent(struct exceptio
atomic_set(&ps->pending_count, 0);
ps->callbacks = NULL;
+ ps->metadata_wq = create_singlethread_workqueue("ksnaphd");
+ if (!ps->metadata_wq) {
+ DMERR("couldn't start header metadata update thread");
+ return -ENOMEM;
+ }
+
store->destroy = persistent_destroy;
store->read_metadata = persistent_read_metadata;
store->prepare_exception = persistent_prepare;
--
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