dm thin: fix passdown_double_checking_shared_status()

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>

diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index 20b0776..ed3cace 100644 (file)
--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -1678,7 +1678,7 @@ int dm_thin_remove_range(struct dm_thin_device *td,
        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;
@@ -1686,7 +1686,7 @@ int dm_pool_block_is_used(struct dm_pool_metadata *pmd, dm_block_t b, bool *resu
        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;

diff --git a/drivers/md/dm-thin-metadata.h b/drivers/md/dm-thin-metadata.h
index 35e954e..f6be0d7 100644 (file)
--- 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 dm_pool_metadata *pmd,
 
 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);

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 1f225a1..c30a785 100644 (file)
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1048,7 +1048,7 @@ static void passdown_double_checking_shared_status(struct dm_thin_new_mapping *m
         * 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;
@@ -1058,11 +1058,11 @@ static void passdown_double_checking_shared_status(struct dm_thin_new_mapping *m
        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;
                }
 
@@ -1071,11 +1071,11 @@ static void passdown_double_checking_shared_status(struct dm_thin_new_mapping *m
 
                /* 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;
                }