[PATCH AUTOSEL for 4.15 123/124] tcmu: release blocks for partially setup cmds

Sasha Levin
2018-03-19T15:50:45Z

From: Mike Christie <mchristi@redhat.com>

[ Upstream commit 810b8153c4243d2012a6ec002ddd3bbc9a9ae8c2 ]

If we cannot setup a cmd because we run out of ring space
or global pages release the blocks before sleeping. This
prevents a deadlock where dev0 has waiting_blocks set and
needs N blocks, but dev1 to devX have each allocated N / X blocks
and also hit the global block limit so they went to sleep.

find_free_blocks is not able to take the sleeping dev's
blocks becaause their waiting_blocks is set and even
if it was not the block returned by find_last_bit could equal
dbi_max. The latter will probably never happen because
DATA_BLOCK_BITS is so high but in the next patches
DATA_BLOCK_BITS and TCMU_GLOBAL_MAX_BLOCKS will be settable so
it might be lower and could happen.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
drivers/target/target_core_user.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index a415d87f22d2..3ab96d0f705e 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -805,6 +805,13 @@ tcmu_queue_cmd_ring(struct tcmu_cmd *tcmu_cmd)
int ret;
DEFINE_WAIT(__wait);

+ /*
+ * Don't leave commands partially setup because the unmap
+ * thread might need the blocks to make forward progress.
+ */
+ tcmu_cmd_free_data(tcmu_cmd, tcmu_cmd->dbi_cur);
+ tcmu_cmd_reset_dbi_cur(tcmu_cmd);
+
prepare_to_wait(&udev->wait_cmdr, &__wait, TASK_INTERRUPTIBLE);

pr_debug("sleeping for ring space\n");
--
2.14.1