| Message ID | 20200918210947.23800-1-leeman.duncan@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | scsi: libiscsi: fix NOP race condition | expand |
On 9/18/20 4:09 PM, Lee Duncan wrote: > From: Lee Duncan <lduncan@suse.com> > > iSCSI NOPs are sometimes "lost", mistakenly sent to the > user-land iscsid daemon instead of handled in the kernel, > as they should be, resulting in a message from the daemon like: > >> iscsid: Got nop in, but kernel supports nop handling. > > This can occur because of the new forward- and back-locks, > and the fact that an iSCSI NOP response can occur before > processing of the NOP send is complete. This can result > in "conn->ping_task" being NULL in iscsi_nop_out_rsp(), > when the pointer is actually in the process of being set. > > To work around this, we add a new state to the "ping_task" > pointer. In addition to NULL (not assigned) and a pointer > (assigned), we add the state "being set", which is signaled > with an INVALID pointer (using "-1"). > > Signed-off-by: Lee Duncan <lduncan@suse.com> > --- > drivers/scsi/libiscsi.c | 11 ++++++++++- > include/scsi/libiscsi.h | 3 +++ > 2 files changed, 13 insertions(+), 1 deletion(-) > > diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c > index 1e9c3171fa9f..5eb064787ee2 100644 > --- a/drivers/scsi/libiscsi.c > +++ b/drivers/scsi/libiscsi.c > @@ -738,6 +738,9 @@ __iscsi_conn_send_pdu(struct iscsi_conn *conn, struct iscsi_hdr *hdr, > task->conn->session->age); > } > > + if (unlikely(READ_ONCE(conn->ping_task) == INVALID_SCSI_TASK)) > + WRITE_ONCE(conn->ping_task, task); > + > if (!ihost->workq) { > if (iscsi_prep_mgmt_task(conn, task)) > goto free_task; > @@ -941,6 +944,11 @@ static int iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr) > struct iscsi_nopout hdr; > struct iscsi_task *task; > > + if (!rhdr) { > + if (READ_ONCE(conn->ping_task)) > + return -EINVAL; > + WRITE_ONCE(conn->ping_task, INVALID_SCSI_TASK); > + } > if (!rhdr && conn->ping_task) > return -EINVAL; > > @@ -957,11 +965,12 @@ static int iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr) > > task = __iscsi_conn_send_pdu(conn, (struct iscsi_hdr *)&hdr, NULL, 0); > if (!task) { > + if (!rhdr) > + WRITE_ONCE(conn->ping_task, NULL); I don't think you need this. If __iscsi_conn_send_pdu returns NULL, it will have done __iscsi_put_task and done this already. > iscsi_conn_printk(KERN_ERR, conn, "Could not send nopout\n"); > return -EIO; > } else if (!rhdr) { > /* only track our nops */ > - conn->ping_task = task; > conn->last_ping = jiffies; > } Why in the send path do we always use the READ_ONCE/WRITE_ONCE, but in the completion path like in iscsi_complete_task we don't.
On 11/4/20 3:33 PM, Mike Christie wrote: > On 9/18/20 4:09 PM, Lee Duncan wrote: >> From: Lee Duncan <lduncan@suse.com> >> >> iSCSI NOPs are sometimes "lost", mistakenly sent to the >> user-land iscsid daemon instead of handled in the kernel, >> as they should be, resulting in a message from the daemon like: >> >>> iscsid: Got nop in, but kernel supports nop handling. >> >> This can occur because of the new forward- and back-locks, >> and the fact that an iSCSI NOP response can occur before >> processing of the NOP send is complete. This can result >> in "conn->ping_task" being NULL in iscsi_nop_out_rsp(), >> when the pointer is actually in the process of being set. >> >> To work around this, we add a new state to the "ping_task" >> pointer. In addition to NULL (not assigned) and a pointer >> (assigned), we add the state "being set", which is signaled >> with an INVALID pointer (using "-1"). >> >> Signed-off-by: Lee Duncan <lduncan@suse.com> >> --- >> drivers/scsi/libiscsi.c | 11 ++++++++++- >> include/scsi/libiscsi.h | 3 +++ >> 2 files changed, 13 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c >> index 1e9c3171fa9f..5eb064787ee2 100644 >> --- a/drivers/scsi/libiscsi.c >> +++ b/drivers/scsi/libiscsi.c >> @@ -738,6 +738,9 @@ __iscsi_conn_send_pdu(struct iscsi_conn *conn, >> struct iscsi_hdr *hdr, >> task->conn->session->age); >> } >> + if (unlikely(READ_ONCE(conn->ping_task) == INVALID_SCSI_TASK)) >> + WRITE_ONCE(conn->ping_task, task); >> + >> if (!ihost->workq) { >> if (iscsi_prep_mgmt_task(conn, task)) >> goto free_task; >> @@ -941,6 +944,11 @@ static int iscsi_send_nopout(struct iscsi_conn >> *conn, struct iscsi_nopin *rhdr) >> struct iscsi_nopout hdr; >> struct iscsi_task *task; >> + if (!rhdr) { >> + if (READ_ONCE(conn->ping_task)) >> + return -EINVAL; >> + WRITE_ONCE(conn->ping_task, INVALID_SCSI_TASK); >> + } >> if (!rhdr && conn->ping_task) >> return -EINVAL; >> @@ -957,11 +965,12 @@ static int iscsi_send_nopout(struct iscsi_conn >> *conn, struct iscsi_nopin *rhdr) >> task = __iscsi_conn_send_pdu(conn, (struct iscsi_hdr *)&hdr, >> NULL, 0); >> if (!task) { >> + if (!rhdr) >> + WRITE_ONCE(conn->ping_task, NULL); > > I don't think you need this. If __iscsi_conn_send_pdu returns NULL, it > will have done __iscsi_put_task and done this already. Ignore that. That is iscsi_complete_task that would do it. > >> iscsi_conn_printk(KERN_ERR, conn, "Could not send nopout\n"); >> return -EIO; >> } else if (!rhdr) { >> /* only track our nops */ >> - conn->ping_task = task; >> conn->last_ping = jiffies; >> } > > Why in the send path do we always use the READ_ONCE/WRITE_ONCE, but in > the completion path like in iscsi_complete_task we don't.
On 11/4/20 1:33 PM, Mike Christie wrote: > On 9/18/20 4:09 PM, Lee Duncan wrote: >> From: Lee Duncan <lduncan@suse.com> >> >> iSCSI NOPs are sometimes "lost", mistakenly sent to the >> user-land iscsid daemon instead of handled in the kernel, >> as they should be, resulting in a message from the daemon like: >> >>> iscsid: Got nop in, but kernel supports nop handling. >> >> This can occur because of the new forward- and back-locks, >> and the fact that an iSCSI NOP response can occur before >> processing of the NOP send is complete. This can result >> in "conn->ping_task" being NULL in iscsi_nop_out_rsp(), >> when the pointer is actually in the process of being set. >> >> To work around this, we add a new state to the "ping_task" >> pointer. In addition to NULL (not assigned) and a pointer >> (assigned), we add the state "being set", which is signaled >> with an INVALID pointer (using "-1"). >> >> Signed-off-by: Lee Duncan <lduncan@suse.com> >> --- >> drivers/scsi/libiscsi.c | 11 ++++++++++- >> include/scsi/libiscsi.h | 3 +++ >> 2 files changed, 13 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c >> index 1e9c3171fa9f..5eb064787ee2 100644 >> --- a/drivers/scsi/libiscsi.c >> +++ b/drivers/scsi/libiscsi.c >> @@ -738,6 +738,9 @@ __iscsi_conn_send_pdu(struct iscsi_conn *conn, >> struct iscsi_hdr *hdr, >> task->conn->session->age); >> } >> + if (unlikely(READ_ONCE(conn->ping_task) == INVALID_SCSI_TASK)) >> + WRITE_ONCE(conn->ping_task, task); >> + >> if (!ihost->workq) { >> if (iscsi_prep_mgmt_task(conn, task)) >> goto free_task; >> @@ -941,6 +944,11 @@ static int iscsi_send_nopout(struct iscsi_conn >> *conn, struct iscsi_nopin *rhdr) >> struct iscsi_nopout hdr; >> struct iscsi_task *task; >> + if (!rhdr) { >> + if (READ_ONCE(conn->ping_task)) >> + return -EINVAL; >> + WRITE_ONCE(conn->ping_task, INVALID_SCSI_TASK); >> + } >> if (!rhdr && conn->ping_task) >> return -EINVAL; >> @@ -957,11 +965,12 @@ static int iscsi_send_nopout(struct iscsi_conn >> *conn, struct iscsi_nopin *rhdr) >> task = __iscsi_conn_send_pdu(conn, (struct iscsi_hdr *)&hdr, >> NULL, 0); >> if (!task) { >> + if (!rhdr) >> + WRITE_ONCE(conn->ping_task, NULL); > > I don't think you need this. If __iscsi_conn_send_pdu returns NULL, it > will have done __iscsi_put_task and done this already. Not an issue, as you already replied. > >> iscsi_conn_printk(KERN_ERR, conn, "Could not send nopout\n"); >> return -EIO; >> } else if (!rhdr) { >> /* only track our nops */ >> - conn->ping_task = task; >> conn->last_ping = jiffies; >> } > > Why in the send path do we always use the READ_ONCE/WRITE_ONCE, but in > the completion path like in iscsi_complete_task we don't. > The answer is that I was only modifying the code that needed changing for this bug. My first pass did not use READ_ONCE() or WRITE_ONCE(), but Hannes suggested the change. Now that I think about it more, the memory barrier stuff would make sense only if all the access to that field are protected. I will resubmit V2 of the patch.
diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c index 1e9c3171fa9f..5eb064787ee2 100644 --- a/drivers/scsi/libiscsi.c +++ b/drivers/scsi/libiscsi.c @@ -738,6 +738,9 @@ __iscsi_conn_send_pdu(struct iscsi_conn *conn, struct iscsi_hdr *hdr, task->conn->session->age); } + if (unlikely(READ_ONCE(conn->ping_task) == INVALID_SCSI_TASK)) + WRITE_ONCE(conn->ping_task, task); + if (!ihost->workq) { if (iscsi_prep_mgmt_task(conn, task)) goto free_task; @@ -941,6 +944,11 @@ static int iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr) struct iscsi_nopout hdr; struct iscsi_task *task; + if (!rhdr) { + if (READ_ONCE(conn->ping_task)) + return -EINVAL; + WRITE_ONCE(conn->ping_task, INVALID_SCSI_TASK); + } if (!rhdr && conn->ping_task) return -EINVAL; @@ -957,11 +965,12 @@ static int iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr) task = __iscsi_conn_send_pdu(conn, (struct iscsi_hdr *)&hdr, NULL, 0); if (!task) { + if (!rhdr) + WRITE_ONCE(conn->ping_task, NULL); iscsi_conn_printk(KERN_ERR, conn, "Could not send nopout\n"); return -EIO; } else if (!rhdr) { /* only track our nops */ - conn->ping_task = task; conn->last_ping = jiffies; } diff --git a/include/scsi/libiscsi.h b/include/scsi/libiscsi.h index c25fb86ffae9..b3bbd10eb3f0 100644 --- a/include/scsi/libiscsi.h +++ b/include/scsi/libiscsi.h @@ -132,6 +132,9 @@ struct iscsi_task { void *dd_data; /* driver/transport data */ }; +/* invalid scsi_task pointer */ +#define INVALID_SCSI_TASK (struct iscsi_task *)-1l + static inline int iscsi_task_has_unsol_data(struct iscsi_task *task) { return task->unsol_r2t.data_length > task->unsol_r2t.sent;