[PATCH 3.12 086/118] dm space map: disallow decrementing a reference count below zero

Greg Kroah-Hartman
2013-12-18T21:16:48Z

From: Joe Thornber <ejt@redhat.com>

commit 5b564d80f8bc21094c0cd2b19b679d983aabcc29 upstream.

The old behaviour, returning -EINVAL if a ref_count of 0 would be
decremented, was removed in commit f722063 ("dm space map: optimise
sm_ll_dec and sm_ll_inc"). To fix this regression we return an error
code from the mutator function pointer passed to sm_ll_mutate() and have
dec_ref_count() return -EINVAL if the old ref_count is 0.

Add a DMERR to reflect the potential seriousness of this error.

Also, add missing dm_tm_unlock() to sm_ll_mutate()'s error path.

With this fix the following dmts regression test now passes:
dmtest run --suite cache -n /metadata_use_kernel/

The next patch fixes the higher-level dm-array code that exposed this
regression.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/persistent-data/dm-space-map-common.c | 32 ++++++++++++++++-------
1 file changed, 23 insertions(+), 9 deletions(-)

--- a/drivers/md/persistent-data/dm-space-map-common.c
+++ b/drivers/md/persistent-data/dm-space-map-common.c
@@ -381,7 +381,7 @@ int sm_ll_find_free_block(struct ll_disk
}

static int sm_ll_mutate(struct ll_disk *ll, dm_block_t b,
- uint32_t (*mutator)(void *context, uint32_t old),
+ int (*mutator)(void *context, uint32_t old, uint32_t *new),
void *context, enum allocation_event *ev)
{
int r;
@@ -410,11 +410,17 @@ static int sm_ll_mutate(struct ll_disk *

if (old > 2) {
r = sm_ll_lookup_big_ref_count(ll, b, &old);
- if (r < 0)
+ if (r < 0) {
+ dm_tm_unlock(ll->tm, nb);
return r;
+ }
}

- ref_count = mutator(context, old);
+ r = mutator(context, old, &ref_count);
+ if (r) {
+ dm_tm_unlock(ll->tm, nb);
+ return r;
+ }

if (ref_count <= 2) {
sm_set_bitmap(bm_le, bit, ref_count);
@@ -465,9 +471,10 @@ static int sm_ll_mutate(struct ll_disk *
return ll->save_ie(ll, index, &ie_disk);
}

-static uint32_t set_ref_count(void *context, uint32_t old)
+static int set_ref_count(void *context, uint32_t old, uint32_t *new)
{
- return *((uint32_t *) context);
+ *new = *((uint32_t *) context);
+ return 0;
}

int sm_ll_insert(struct ll_disk *ll, dm_block_t b,
@@ -476,9 +483,10 @@ int sm_ll_insert(struct ll_disk *ll, dm_
return sm_ll_mutate(ll, b, set_ref_count, &ref_count, ev);
}

-static uint32_t inc_ref_count(void *context, uint32_t old)
+static int inc_ref_count(void *context, uint32_t old, uint32_t *new)
{
- return old + 1;
+ *new = old + 1;
+ return 0;
}

int sm_ll_inc(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev)
@@ -486,9 +494,15 @@ int sm_ll_inc(struct ll_disk *ll, dm_blo
return sm_ll_mutate(ll, b, inc_ref_count, NULL, ev);
}

-static uint32_t dec_ref_count(void *context, uint32_t old)
+static int dec_ref_count(void *context, uint32_t old, uint32_t *new)
{
- return old - 1;
+ if (!old) {
+ DMERR_LIMIT("unable to decrement a reference count below 0");
+ return -EINVAL;
+ }
+
+ *new = old - 1;
+ return 0;
}

int sm_ll_dec(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev)