[PATCH 12/19] libfc: Do not invoke the response handler after fc_exch_done()

Robert Love
2013-10-21T18:01:34Z

While the FCoE initiator driver invokes fc_exch_done() from inside
the libfc response handler, FCoE target drivers typically invoke
fc_exch_done() from outside the libfc response handler. The object
fc_exch.arg points at may disappear as soon as fc_exch_done() has
finished. So it's important not to invoke the response handler
function after fc_exch_done() has finished. Modify libfc such that
this guarantee is provided if fc_exch_done() is invoked from
outside a response handler. This patch fixes a sporadic crash in
FCoE target implementations after a command has been aborted.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
---
drivers/scsi/libfc/fc_exch.c | 131 +++++++++++++++++++++++++++++-------------
include/scsi/libfc.h | 9 +++
2 files changed, 101 insertions(+), 39 deletions(-)

diff --git a/drivers/scsi/libfc/fc_exch.c b/drivers/scsi/libfc/fc_exch.c
index 47ebc7b..1b3a094 100644
--- a/drivers/scsi/libfc/fc_exch.c
+++ b/drivers/scsi/libfc/fc_exch.c
@@ -381,6 +381,8 @@ static void fc_exch_timer_set(struct fc_exch *ep, unsigned int timer_msec)
/**
* fc_exch_done_locked() - Complete an exchange with the exchange lock held
* @ep: The exchange that is complete
+ *
+ * Note: May sleep if invoked from outside a response handler.
*/
static int fc_exch_done_locked(struct fc_exch *ep)
{
@@ -392,7 +394,6 @@ static int fc_exch_done_locked(struct fc_exch *ep)
* ep, and in that case we only clear the resp and set it as
* complete, so it can be reused by the timer to send the rrq.
*/
- ep->resp = NULL;
if (ep->state & FC_EX_DONE)
return rc;
ep->esb_stat |= ESB_ST_COMPLETE;
@@ -589,6 +590,8 @@ static struct fc_seq *fc_seq_start_next(struct fc_seq *sp)

/*
* Set the response handler for the exchange associated with a sequence.
+ *
+ * Note: May sleep if invoked from outside a response handler.
*/
static void fc_seq_set_resp(struct fc_seq *sp,
void (*resp)(struct fc_seq *, struct fc_frame *,
@@ -596,8 +599,18 @@ static void fc_seq_set_resp(struct fc_seq *sp,
void *arg)
{
struct fc_exch *ep = fc_seq_exch(sp);
+ DEFINE_WAIT(wait);

spin_lock_bh(&ep->ex_lock);
+ while (ep->resp_active && ep->resp_task != current) {
+ prepare_to_wait(&ep->resp_wq, &wait, TASK_UNINTERRUPTIBLE);
+ spin_unlock_bh(&ep->ex_lock);
+
+ schedule();
+
+ spin_lock_bh(&ep->ex_lock);
+ }
+ finish_wait(&ep->resp_wq, &wait);
ep->resp = resp;
ep->arg = arg;
spin_unlock_bh(&ep->ex_lock);
@@ -681,6 +694,61 @@ static int fc_seq_exch_abort(const struct fc_seq *req_sp,
}

/**
+ * fc_invoke_resp() - invoke ep->resp()
+ *
+ * Notes:
+ * It is assumed that after initialization finished (this means the
+ * first unlock of ex_lock after fc_exch_alloc()) ep->resp and ep->arg are
+ * modified only via fc_seq_set_resp(). This guarantees that none of these
+ * two variables changes if ep->resp_active > 0.
+ *
+ * If an fc_seq_set_resp() call is busy modifying ep->resp and ep->arg when
+ * this function is invoked, the first spin_lock_bh() call in this function
+ * will wait until fc_seq_set_resp() has finished modifying these variables.
+ *
+ * Since fc_exch_done() invokes fc_seq_set_resp() it is guaranteed that that
+ * ep->resp() won't be invoked after fc_exch_done() has returned.
+ *
+ * The response handler itself may invoke fc_exch_done(), which will clear the
+ * ep->resp pointer.
+ *
+ * Return value:
+ * Returns true if and only if ep->resp has been invoked.
+ */
+static bool fc_invoke_resp(struct fc_exch *ep, struct fc_seq *sp,
+ struct fc_frame *fp)
+{
+ void (*resp)(struct fc_seq *, struct fc_frame *fp, void *arg);
+ void *arg;
+ bool res = false;
+
+ spin_lock_bh(&ep->ex_lock);
+ ep->resp_active++;
+ if (ep->resp_task != current)
+ ep->resp_task = !ep->resp_task ? current : NULL;
+ resp = ep->resp;
+ arg = ep->arg;
+ spin_unlock_bh(&ep->ex_lock);
+
+ if (resp) {
+ resp(sp, fp, arg);
+ res = true;
+ } else if (!IS_ERR(fp)) {
+ fc_frame_free(fp);
+ }
+
+ spin_lock_bh(&ep->ex_lock);
+ if (--ep->resp_active == 0)
+ ep->resp_task = NULL;
+ spin_unlock_bh(&ep->ex_lock);
+
+ if (ep->resp_active == 0)
+ wake_up(&ep->resp_wq);
+
+ return res;
+}
+
+/**
* fc_exch_timeout() - Handle exchange timer expiration
* @work: The work_struct identifying the exchange that timed out
*/
@@ -689,8 +757,6 @@ static void fc_exch_timeout(struct work_struct *work)
struct fc_exch *ep = container_of(work, struct fc_exch,
timeout_work.work);
struct fc_seq *sp = &ep->seq;
- void (*resp)(struct fc_seq *, struct fc_frame *fp, void *arg);
- void *arg;
u32 e_stat;
int rc = 1;

@@ -708,16 +774,13 @@ static void fc_exch_timeout(struct work_struct *work)
fc_exch_rrq(ep);
goto done;
} else {
- resp = ep->resp;
- arg = ep->arg;
- ep->resp = NULL;
if (e_stat & ESB_ST_ABNORMAL)
rc = fc_exch_done_locked(ep);
spin_unlock_bh(&ep->ex_lock);
if (!rc)
fc_exch_delete(ep);
- if (resp)
- resp(sp, ERR_PTR(-FC_EX_TIMEOUT), arg);
+ fc_invoke_resp(ep, sp, ERR_PTR(-FC_EX_TIMEOUT));
+ fc_seq_set_resp(sp, NULL, ep->arg);
fc_seq_exch_abort(sp, 2 * ep->r_a_tov);
goto done;
}
@@ -804,6 +867,8 @@ hit:
ep->f_ctl = FC_FC_FIRST_SEQ; /* next seq is first seq */
ep->rxid = FC_XID_UNKNOWN;
ep->class = mp->class;
+ ep->resp_active = 0;
+ init_waitqueue_head(&ep->resp_wq);
INIT_DELAYED_WORK(&ep->timeout_work, fc_exch_timeout);
out:
return ep;
@@ -864,6 +929,8 @@ static struct fc_exch *fc_exch_find(struct fc_exch_mgr *mp, u16 xid)
* fc_exch_done() - Indicate that an exchange/sequence tuple is complete and
* the memory allocated for the related objects may be freed.
* @sp: The sequence that has completed
+ *
+ * Note: May sleep if invoked from outside a response handler.
*/
static void fc_exch_done(struct fc_seq *sp)
{
@@ -873,6 +940,8 @@ static void fc_exch_done(struct fc_seq *sp)
spin_lock_bh(&ep->ex_lock);
rc = fc_exch_done_locked(ep);
spin_unlock_bh(&ep->ex_lock);
+
+ fc_seq_set_resp(sp, NULL, ep->arg);
if (!rc)
fc_exch_delete(ep);
}
@@ -1436,9 +1505,7 @@ static void fc_exch_recv_req(struct fc_lport *lport, struct fc_exch_mgr *mp,
* If new exch resp handler is valid then call that
* first.
*/
- if (ep->resp)
- ep->resp(sp, fp, ep->arg);
- else
+ if (!fc_invoke_resp(ep, sp, fp))
lport->tt.lport_recv(lport, fp);
fc_exch_release(ep); /* release from lookup */
} else {
@@ -1462,8 +1529,6 @@ static void fc_exch_recv_seq_resp(struct fc_exch_mgr *mp, struct fc_frame *fp)
struct fc_exch *ep;
enum fc_sof sof;
u32 f_ctl;
- void (*resp)(struct fc_seq *, struct fc_frame *fp, void *arg);
- void *ex_resp_arg;
int rc;

ep = fc_exch_find(mp, ntohs(fh->fh_ox_id));
@@ -1506,14 +1571,11 @@ static void fc_exch_recv_seq_resp(struct fc_exch_mgr *mp, struct fc_frame *fp)

if (fc_sof_needs_ack(sof))
fc_seq_send_ack(sp, fp);
- resp = ep->resp;
- ex_resp_arg = ep->arg;

if (fh->fh_type != FC_TYPE_FCP && fr_eof(fp) == FC_EOF_T &&
(f_ctl & (FC_FC_LAST_SEQ | FC_FC_END_SEQ)) ==
(FC_FC_LAST_SEQ | FC_FC_END_SEQ)) {
spin_lock_bh(&ep->ex_lock);
- resp = ep->resp;
rc = fc_exch_done_locked(ep);
WARN_ON(fc_seq_exch(sp) != ep);
spin_unlock_bh(&ep->ex_lock);
@@ -1534,10 +1596,8 @@ static void fc_exch_recv_seq_resp(struct fc_exch_mgr *mp, struct fc_frame *fp)
* If new exch resp handler is valid then call that
* first.
*/
- if (resp)
- resp(sp, fp, ex_resp_arg);
- else
- fc_frame_free(fp);
+ fc_invoke_resp(ep, sp, fp);
+
fc_exch_release(ep);
return;
rel:
@@ -1576,8 +1636,6 @@ static void fc_exch_recv_resp(struct fc_exch_mgr *mp, struct fc_frame *fp)
*/
static void fc_exch_abts_resp(struct fc_exch *ep, struct fc_frame *fp)
{
- void (*resp)(struct fc_seq *, struct fc_frame *fp, void *arg);
- void *ex_resp_arg;
struct fc_frame_header *fh;
struct fc_ba_acc *ap;
struct fc_seq *sp;
@@ -1622,9 +1680,6 @@ static void fc_exch_abts_resp(struct fc_exch *ep, struct fc_frame *fp)
break;
}

- resp = ep->resp;
- ex_resp_arg = ep->arg;
-
/* do we need to do some other checks here. Can we reuse more of
* fc_exch_recv_seq_resp
*/
@@ -1636,17 +1691,14 @@ static void fc_exch_abts_resp(struct fc_exch *ep, struct fc_frame *fp)
ntoh24(fh->fh_f_ctl) & FC_FC_LAST_SEQ)
rc = fc_exch_done_locked(ep);
spin_unlock_bh(&ep->ex_lock);
+
+ fc_exch_hold(ep);
if (!rc)
fc_exch_delete(ep);
-
- if (resp)
- resp(sp, fp, ex_resp_arg);
- else
- fc_frame_free(fp);
-
+ fc_invoke_resp(ep, sp, fp);
if (has_rec)
fc_exch_timer_set(ep, ep->r_a_tov);
-
+ fc_exch_release(ep);
}

/**
@@ -1768,32 +1820,33 @@ static void fc_seq_ls_rjt(struct fc_frame *rx_fp, enum fc_els_rjt_reason reason,
/**
* fc_exch_reset() - Reset an exchange
* @ep: The exchange to be reset
+ *
+ * Note: May sleep if invoked from outside a response handler.
*/
static void fc_exch_reset(struct fc_exch *ep)
{
struct fc_seq *sp;
- void (*resp)(struct fc_seq *, struct fc_frame *, void *);
- void *arg;
int rc = 1;

spin_lock_bh(&ep->ex_lock);
fc_exch_abort_locked(ep, 0);
ep->state |= FC_EX_RST_CLEANUP;
fc_exch_timer_cancel(ep);
- resp = ep->resp;
- ep->resp = NULL;
if (ep->esb_stat & ESB_ST_REC_QUAL)
atomic_dec(&ep->ex_refcnt); /* drop hold for rec_qual */
ep->esb_stat &= ~ESB_ST_REC_QUAL;
- arg = ep->arg;
sp = &ep->seq;
rc = fc_exch_done_locked(ep);
spin_unlock_bh(&ep->ex_lock);
+
+ fc_exch_hold(ep);
+
if (!rc)
fc_exch_delete(ep);

- if (resp)
- resp(sp, ERR_PTR(-FC_EX_CLOSED), arg);
+ fc_invoke_resp(ep, sp, ERR_PTR(-FC_EX_CLOSED));
+ fc_seq_set_resp(sp, NULL, ep->arg);
+ fc_exch_release(ep);
}

/**
diff --git a/include/scsi/libfc.h b/include/scsi/libfc.h
index e1379b4..52beadf 100644
--- a/include/scsi/libfc.h
+++ b/include/scsi/libfc.h
@@ -410,6 +410,12 @@ struct fc_seq {
* @fh_type: The frame type
* @class: The class of service
* @seq: The sequence in use on this exchange
+ * @resp_active: Number of tasks that are concurrently executing @resp().
+ * @resp_task: If @resp_active > 0, either the task executing @resp(), the
+ * task that has been interrupted to execute the soft-IRQ
+ * executing @resp() or NULL if more than one task is executing
+ * @resp concurrently.
+ * @resp_wq: Waitqueue for the tasks waiting on @resp_active.
* @resp: Callback for responses on this exchange
* @destructor: Called when destroying the exchange
* @arg: Passed as a void pointer to the resp() callback
@@ -441,6 +447,9 @@ struct fc_exch {
u32 r_a_tov;
u32 f_ctl;
struct fc_seq seq;
+ int resp_active;
+ struct task_struct *resp_task;
+ wait_queue_head_t resp_wq;
void (*resp)(struct fc_seq *, struct fc_frame *, void *);
void *arg;
void (*destructor)(struct fc_seq *, void *);