Re: dm transaction manager: handle space map checker failure

[Mike Snitzer <snitzer@redhat.com>]

On Wed, Jun 20 2012 at  6:15pm -0400,
Mike Snitzer <snitzer@redhat.com> wrote:

> On Wed, Jun 20 2012 at  5:37pm -0400,
> Vivek Goyal <vgoyal@redhat.com> wrote:
> 
> > On Wed, Jun 20, 2012 at 05:20:10PM -0400, Vivek Goyal wrote:
> > > On Wed, Jun 20, 2012 at 03:24:59PM -0400, Mike Snitzer wrote:
> > > > If CONFIG_DM_DEBUG_SPACE_MAPS is enabled and dm_sm_checker_create()
> > > > fails, dm_tm_create_internal() would still return success even though it
> > > > cleaned up all resources it was supposed to have created.
> > > > 
> > > > Fix the space map checker code to return an appropriate ERR_PTR and have
> > > > dm_tm_create_internal() check for it with IS_ERR.
> > > > 
> > > 
> > > I tested the patch and it works. It fails gracefully instead of segfaulting.
> > > 
> > > device-mapper: reload ioctl failed: Cannot allocate memory
> > > 
> > > I still do get waring though about large memory allocation. That's a
> > > separate issue though.
> > 
> > I put a trace_printk() in ca_create() to see how much memory we are trying
> > to allocated using kzalloc. And answer is 10485760. Number of blocks
> > obtained from space map is 2621440. I think this might be happening because 
> > my metadata device size is 10G.
> 
> It is.  My metadata device is 1G and I'm seeing nr_blocks=262144
> 
> So kzalloc on your system cannot find 10M of contiguous memory.
> 
> How does this patch work for you?

Hey Vivek,

Here is a more comprehensive patch (seems vmalloc doesn't support
passing a @size of 0, whereas kmalloc does).

But I know that this patch causes sm_checker_destroy() to crash in the
kfree() from ca_destroy(&smc->old_counts);

If I simply switch back from vzalloc to using kzalloc all works fine!?

Seems very odd, will dig deeper when I get a chance.

commit 65f1ea9401aeec7618626c3c32defbee5db30deb
Author: Mike Snitzer <snitzer@redhat.com>
Date:   Thu Jun 21 00:05:18 2012 -0400

    dm space map: fix error path of space map checker creation

diff --git a/drivers/md/persistent-data/dm-space-map-checker.c b/drivers/md/persistent-data/dm-space-map-checker.c
index 6d7c832..d4463dc 100644
--- a/drivers/md/persistent-data/dm-space-map-checker.c
+++ b/drivers/md/persistent-data/dm-space-map-checker.c
@@ -89,9 +89,13 @@ static int ca_create(struct count_array *ca, struct dm_space_map *sm)
 
 	ca->nr = nr_blocks;
 	ca->nr_free = nr_blocks;
-	ca->counts = kzalloc(sizeof(*ca->counts) * nr_blocks, GFP_KERNEL);
-	if (!ca->counts)
-		return -ENOMEM;
+
+	if (nr_blocks) {
+		ca->counts = vzalloc(sizeof(*ca->counts) * nr_blocks);
+		if (!ca->counts)
+			return -ENOMEM;
+	} else
+		ca->counts = NULL;
 
 	return 0;
 }
@@ -126,12 +130,14 @@ static int ca_load(struct count_array *ca, struct dm_space_map *sm)
 static int ca_extend(struct count_array *ca, dm_block_t extra_blocks)
 {
 	dm_block_t nr_blocks = ca->nr + extra_blocks;
-	uint32_t *counts = kzalloc(sizeof(*counts) * nr_blocks, GFP_KERNEL);
+	uint32_t *counts = vzalloc(sizeof(*counts) * nr_blocks);
 	if (!counts)
 		return -ENOMEM;
 
-	memcpy(counts, ca->counts, sizeof(*counts) * ca->nr);
-	kfree(ca->counts);
+	if (ca->counts) {
+		memcpy(counts, ca->counts, sizeof(*counts) * ca->nr);
+		kfree(ca->counts);
+	}
 	ca->nr = nr_blocks;
 	ca->nr_free += extra_blocks;
 	ca->counts = counts;
diff --git a/drivers/md/persistent-data/dm-space-map-disk.c b/drivers/md/persistent-data/dm-space-map-disk.c
index 9535234..124828b 100644
--- a/drivers/md/persistent-data/dm-space-map-disk.c
+++ b/drivers/md/persistent-data/dm-space-map-disk.c
@@ -315,7 +315,13 @@ struct dm_space_map *dm_sm_disk_create(struct dm_transaction_manager *tm,
 				       dm_block_t nr_blocks)
 {
 	struct dm_space_map *sm = dm_sm_disk_create_real(tm, nr_blocks);
-	return dm_sm_checker_create_fresh(sm);
+	struct dm_space_map *smc = dm_sm_checker_create_fresh(sm);
+
+	if (IS_ERR(smc) && !IS_ERR_OR_NULL(sm))
+		dm_sm_destroy(sm);
+	sm = smc;
+
+	return sm;
 }
 EXPORT_SYMBOL_GPL(dm_sm_disk_create);