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Commit f56574a2 authored by Andy Grover's avatar Andy Grover Committed by Nicholas Bellinger
Browse files

target/user: Recalculate pad size inside is_ring_space_avail() 



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: default avatarAndy Grover <agrover@redhat.com>
Signed-off-by: default avatarNicholas Bellinger <nab@linux-iscsi.org>
parent 6375f890

drivers/target/target_core_user.c

+16 −15
Original line number Diff line number Diff line
@@ -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);