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[SCSI] iscsi_tcp: fix potential lockup with write commands

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There is a race condition in iscsi_tcp.c that may cause it to forget
that it received a R2T from the target.  This race may cause a data-out
command (such as a write) to lock up.  The race occurs here:

static int
iscsi_send_unsol_pdu(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
{
	struct iscsi_tcp_cmd_task *tcp_ctask = ctask->dd_data;
	int rc;

	if (tcp_ctask->xmstate & XMSTATE_UNS_HDR) {
		BUG_ON(!ctask->unsol_count);
		tcp_ctask->xmstate &= ~XMSTATE_UNS_HDR; <---- RACE
		...

static int
iscsi_r2t_rsp(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
{
	...
	tcp_ctask->xmstate |= XMSTATE_SOL_HDR_INIT; <---- RACE
	...

While iscsi_xmitworker() (called from scsi_queue_work()) is preparing to
send unsolicited data, iscsi_tcp_data_recv() (called from
tcp_read_sock()) interrupts it upon receipt of a R2T from the target.
Both contexts do read-modify-write of tcp_ctask->xmstate.  Usually, gcc
on x86 will make &= and |= atomic on UP (not guaranteed of course), but
in this case iscsi_send_unsol_pdu() reads the value of xmstate before
clearing the bit, which causes gcc to read xmstate into a CPU register,
test it, clear the bit, and then store it back to memory.  If the recv
interrupt happens during this sequence, then the XMSTATE_SOL_HDR_INIT
bit set by the recv interrupt will be lost, and the R2T will be
forgotten.

The patch below (against 2.6.24-rc1) converts accesses of xmstate to use
set_bit, clear_bit, and test_bit instead of |= and &=.  I have tested
this patch and verified that it fixes the problem.  Another possible
approach would be to hold a lock during most of the rx/tx setup and
post-processing, and drop the lock only for the actual rx/tx.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
This commit is contained in:
Tony Battersby
2007-11-14 14:38:42 -06:00
committed by James Bottomley
parent 5f78e89b5f
commit 505f76b306
2 changed files with 86 additions and 87 deletions
Download Patch File Download Diff File Expand all files Collapse all files

34
drivers/scsi/iscsi_tcp.h
View File

@@ -32,21 +32,21 @@
#define IN_PROGRESS_PAD_RECV 0x4
/* xmit state machine */
#define XMSTATE_IDLE 0x0
#define XMSTATE_CMD_HDR_INIT 0x1
#define XMSTATE_CMD_HDR_XMIT 0x2
#define XMSTATE_IMM_HDR 0x4
#define XMSTATE_IMM_DATA 0x8
#define XMSTATE_UNS_INIT 0x10
#define XMSTATE_UNS_HDR 0x20
#define XMSTATE_UNS_DATA 0x40
#define XMSTATE_SOL_HDR 0x80
#define XMSTATE_SOL_DATA 0x100
#define XMSTATE_W_PAD 0x200
#define XMSTATE_W_RESEND_PAD 0x400
#define XMSTATE_W_RESEND_DATA_DIGEST 0x800
#define XMSTATE_IMM_HDR_INIT 0x1000
#define XMSTATE_SOL_HDR_INIT 0x2000
#define XMSTATE_VALUE_IDLE 0
#define XMSTATE_BIT_CMD_HDR_INIT 0
#define XMSTATE_BIT_CMD_HDR_XMIT 1
#define XMSTATE_BIT_IMM_HDR 2
#define XMSTATE_BIT_IMM_DATA 3
#define XMSTATE_BIT_UNS_INIT 4
#define XMSTATE_BIT_UNS_HDR 5
#define XMSTATE_BIT_UNS_DATA 6
#define XMSTATE_BIT_SOL_HDR 7
#define XMSTATE_BIT_SOL_DATA 8
#define XMSTATE_BIT_W_PAD 9
#define XMSTATE_BIT_W_RESEND_PAD 10
#define XMSTATE_BIT_W_RESEND_DATA_DIGEST 11
#define XMSTATE_BIT_IMM_HDR_INIT 12
#define XMSTATE_BIT_SOL_HDR_INIT 13
#define ISCSI_PAD_LEN 4
#define ISCSI_SG_TABLESIZE SG_ALL
@@ -122,7 +122,7 @@ struct iscsi_data_task {
struct iscsi_tcp_mgmt_task {
struct iscsi_hdr hdr;
char hdrext[sizeof(__u32)]; /* Header-Digest */
int xmstate; /* mgmt xmit progress */
unsigned long xmstate; /* mgmt xmit progress */
struct iscsi_buf headbuf; /* header buffer */
struct iscsi_buf sendbuf; /* in progress buffer */
int sent;
@@ -150,7 +150,7 @@ struct iscsi_tcp_cmd_task {
int pad_count; /* padded bytes */
struct iscsi_buf headbuf; /* header buf (xmit) */
struct iscsi_buf sendbuf; /* in progress buffer*/
int xmstate; /* xmit xtate machine */
unsigned long xmstate; /* xmit xtate machine */
int sent;
struct scatterlist *sg; /* per-cmd SG list */
struct scatterlist *bad_sg; /* assert statement */