From 505f76b3061f6e74a50f378e45ac931abc1fe784 Mon Sep 17 00:00:00 2001 From: Tony Battersby Date: Wed, 14 Nov 2007 14:38:42 -0600 Subject: [SCSI] iscsi_tcp: fix potential lockup with write commands 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 Signed-off-by: Mike Christie Signed-off-by: James Bottomley --- drivers/scsi/iscsi_tcp.h | 34 +++++++++++++++++----------------- 1 file changed, 17 insertions(+), 17 deletions(-) (limited to 'drivers/scsi/iscsi_tcp.h') diff --git a/drivers/scsi/iscsi_tcp.h b/drivers/scsi/iscsi_tcp.h index 7eba44df0a7f..68c36cc8997e 100644 --- a/drivers/scsi/iscsi_tcp.h +++ b/drivers/scsi/iscsi_tcp.h @@ -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 */ -- cgit v1.2.3