If more than one thread is waiting for command ring space that includes
a PAD, then if the first one finishes (inserts a PAD and a CMD at the
start of the cmd ring) then the second one will incorrectly think it still
needs to insert a PAD (i.e. cmdr_space_needed is now wrong.) This will
lead to it asking for more space than it actually needs, and then inserting
a PAD somewhere else than at the end -- not what we want.
This patch moves the pad calculation inside is_ring_space_available() so
in the above scenario the second thread would then ask for space not
including a PAD. The patch also inserts a PAD op based upon an up-to-date
cmd_head, instead of the potentially stale value.
Signed-off-by: Andy Grover <agrover@xxxxxxxxxx>
---
drivers/target/target_core_user.c | 31 ++++++++++++++++---------------
1 file changed, 16 insertions(+), 15 deletions(-)
diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index c52b592..f798e80 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -236,16 +236,26 @@ static inline size_t head_to_end(size_t head, size_t size)
*
* Called with ring lock held.
*/
-static bool is_ring_space_avail(struct tcmu_dev *udev, size_t cmd_needed, size_t data_needed)
+static bool is_ring_space_avail(struct tcmu_dev *udev, size_t cmd_size, size_t data_needed)
{
struct tcmu_mailbox *mb = udev->mb_addr;
size_t space;
u32 cmd_head;
+ size_t cmd_needed;
tcmu_flush_dcache_range(mb, sizeof(*mb));
cmd_head = mb->cmd_head % udev->cmdr_size; /* UAM */
+ /*
+ * If cmd end-of-ring space is too small then we need space for a NOP plus
+ * original cmd - cmds are internally contiguous.
+ */
+ if (head_to_end(cmd_head, udev->cmdr_size) >= cmd_size)
+ cmd_needed = cmd_size;
+ else
+ cmd_needed = cmd_size + head_to_end(cmd_head, udev->cmdr_size);
+
space = spc_free(cmd_head, udev->cmdr_last_cleaned, udev->cmdr_size);
if (space < cmd_needed) {
pr_debug("no cmd space: %u %u %u\n", cmd_head,
@@ -268,9 +278,7 @@ static int tcmu_queue_cmd_ring(struct tcmu_cmd *tcmu_cmd)
struct tcmu_dev *udev = tcmu_cmd->tcmu_dev;
struct se_cmd *se_cmd = tcmu_cmd->se_cmd;
size_t base_command_size, command_size;
- size_t cmdr_space_needed;
struct tcmu_mailbox *mb;
- size_t pad_size;
struct tcmu_cmd_entry *entry;
int i;
struct scatterlist *sg;
@@ -307,17 +315,7 @@ static int tcmu_queue_cmd_ring(struct tcmu_cmd *tcmu_cmd)
"cmd/data ring buffers\n", command_size, tcmu_cmd->data_length,
udev->cmdr_size, udev->data_size);
- /*
- * Cmd end-of-ring space is too small so we need space for a NOP plus
- * original cmd - cmds are internally contiguous.
- */
- if (head_to_end(cmd_head, udev->cmdr_size) >= command_size)
- pad_size = 0;
- else
- pad_size = head_to_end(cmd_head, udev->cmdr_size);
- cmdr_space_needed = command_size + pad_size;
-
- while (!is_ring_space_avail(udev, cmdr_space_needed, tcmu_cmd->data_length)) {
+ while (!is_ring_space_avail(udev, command_size, tcmu_cmd->data_length)) {
int ret;
DEFINE_WAIT(__wait);
@@ -338,7 +336,10 @@ static int tcmu_queue_cmd_ring(struct tcmu_cmd *tcmu_cmd)
cmd_head = mb->cmd_head % udev->cmdr_size; /* UAM */
}
- if (pad_size) {
+ /* Insert a PAD if end-of-ring space is too small */
+ if (head_to_end(cmd_head, udev->cmdr_size) < command_size) {
+ size_t pad_size = head_to_end(cmd_head, udev->cmdr_size);
+
entry = (void *) mb + CMDR_OFF + cmd_head;
tcmu_flush_dcache_range(entry, sizeof(*entry));
tcmu_hdr_set_op(&entry->hdr, TCMU_OP_PAD);
--
1.9.3
--
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