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Subject[PATCH 4.9 29/44] dm thin: fix passdown_double_checking_shared_status()
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joe Thornber <ejt@redhat.com>

commit d445bd9cec1a850c2100fcf53684c13b3fd934f2 upstream.

Commit 00a0ea33b495 ("dm thin: do not queue freed thin mapping for next
stage processing") changed process_prepared_discard_passdown_pt1() to
increment all the blocks being discarded until after the passdown had
completed to avoid them being prematurely reused.

IO issued to a thin device that breaks sharing with a snapshot, followed
by a discard issued to snapshot(s) that previously shared the block(s),
results in passdown_double_checking_shared_status() being called to
iterate through the blocks double checking their reference count is zero
and issuing the passdown if so. So a side effect of commit 00a0ea33b495
is passdown_double_checking_shared_status() was broken.

Fix this by checking if the block reference count is greater than 1.
Also, rename dm_pool_block_is_used() to dm_pool_block_is_shared().

Fixes: 00a0ea33b495 ("dm thin: do not queue freed thin mapping for next stage processing")
Cc: stable@vger.kernel.org # 4.9+
Reported-by: ryan.p.norwood@gmail.com
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/dm-thin-metadata.c | 4 ++--
drivers/md/dm-thin-metadata.h | 2 +-
drivers/md/dm-thin.c | 10 +++++-----
3 files changed, 8 insertions(+), 8 deletions(-)

--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -1689,7 +1689,7 @@ int dm_thin_remove_range(struct dm_thin_
return r;
}

-int dm_pool_block_is_used(struct dm_pool_metadata *pmd, dm_block_t b, bool *result)
+int dm_pool_block_is_shared(struct dm_pool_metadata *pmd, dm_block_t b, bool *result)
{
int r;
uint32_t ref_count;
@@ -1697,7 +1697,7 @@ int dm_pool_block_is_used(struct dm_pool
down_read(&pmd->root_lock);
r = dm_sm_get_count(pmd->data_sm, b, &ref_count);
if (!r)
- *result = (ref_count != 0);
+ *result = (ref_count > 1);
up_read(&pmd->root_lock);

return r;
--- a/drivers/md/dm-thin-metadata.h
+++ b/drivers/md/dm-thin-metadata.h
@@ -195,7 +195,7 @@ int dm_pool_get_metadata_dev_size(struct

int dm_pool_get_data_dev_size(struct dm_pool_metadata *pmd, dm_block_t *result);

-int dm_pool_block_is_used(struct dm_pool_metadata *pmd, dm_block_t b, bool *result);
+int dm_pool_block_is_shared(struct dm_pool_metadata *pmd, dm_block_t b, bool *result);

int dm_pool_inc_data_range(struct dm_pool_metadata *pmd, dm_block_t b, dm_block_t e);
int dm_pool_dec_data_range(struct dm_pool_metadata *pmd, dm_block_t b, dm_block_t e);
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1017,7 +1017,7 @@ static void passdown_double_checking_sha
* passdown we have to check that these blocks are now unused.
*/
int r = 0;
- bool used = true;
+ bool shared = true;
struct thin_c *tc = m->tc;
struct pool *pool = tc->pool;
dm_block_t b = m->data_block, e, end = m->data_block + m->virt_end - m->virt_begin;
@@ -1027,11 +1027,11 @@ static void passdown_double_checking_sha
while (b != end) {
/* find start of unmapped run */
for (; b < end; b++) {
- r = dm_pool_block_is_used(pool->pmd, b, &used);
+ r = dm_pool_block_is_shared(pool->pmd, b, &shared);
if (r)
goto out;

- if (!used)
+ if (!shared)
break;
}

@@ -1040,11 +1040,11 @@ static void passdown_double_checking_sha

/* find end of run */
for (e = b + 1; e != end; e++) {
- r = dm_pool_block_is_used(pool->pmd, e, &used);
+ r = dm_pool_block_is_shared(pool->pmd, e, &shared);
if (r)
goto out;

- if (used)
+ if (shared)
break;
}


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