In the context of FRMR (ib_frmr.c):
Memory regions make it onto the "clean_list" via "rds_ib_flush_mr_pool",
after the memory region has been posted for invalidation via
"rds_ib_post_inv".
At that point in time, "fr_state" may still be in state "FRMR_IS_INUSE",
since the only place where "fr_state" transitions to "FRMR_IS_FREE"
is in "rds_ib_mr_cqe_handler", which is triggered by a tasklet.
So in case we notice that "fr_state != FRMR_IS_FREE" (see below),
we wait for "fr_inv_done" to trigger with a maximum of 10msec.
Then we check again, and only put the memory region onto the drop_list
(via "rds_ib_free_frmr") in case the situation remains unchanged.
This avoids the problem of memory-regions bouncing between "clean_list"
and "drop_list" before they even have a chance to be properly invalidated.
Signed-off-by: Gerd Rausch <gerd.rausch@xxxxxxxxxx>
---
net/rds/ib_frmr.c | 27 ++++++++++++++++++++++++++-
net/rds/ib_mr.h | 1 +
2 files changed, 27 insertions(+), 1 deletion(-)
diff --git a/net/rds/ib_frmr.c b/net/rds/ib_frmr.c
index 32ae26ed58a0..6038138d6e38 100644
--- a/net/rds/ib_frmr.c
+++ b/net/rds/ib_frmr.c
@@ -75,6 +75,7 @@ static struct rds_ib_mr *rds_ib_alloc_frmr(struct rds_ib_device *rds_ibdev,
pool->max_items_soft = pool->max_items;
frmr->fr_state = FRMR_IS_FREE;
+ init_waitqueue_head(&frmr->fr_inv_done);
return ibmr;
out_no_cigar:
@@ -285,6 +286,7 @@ void rds_ib_mr_cqe_handler(struct rds_ib_connection *ic, struct ib_wc *wc)
if (frmr->fr_inv) {
frmr->fr_state = FRMR_IS_FREE;
frmr->fr_inv = false;
+ wake_up(&frmr->fr_inv_done);
}
atomic_inc(&ic->i_fastreg_wrs);
@@ -345,8 +347,31 @@ struct rds_ib_mr *rds_ib_reg_frmr(struct rds_ib_device *rds_ibdev,
}
do {
- if (ibmr)
+ if (ibmr) {
+ /* Memory regions make it onto the "clean_list" via
+ * "rds_ib_flush_mr_pool", after the memory region has
+ * been posted for invalidation via "rds_ib_post_inv".
+ *
+ * At that point in time, "fr_state" may still be
+ * in state "FRMR_IS_INUSE", since the only place where
+ * "fr_state" transitions to "FRMR_IS_FREE" is in
+ * is in "rds_ib_mr_cqe_handler", which is
+ * triggered by a tasklet.
+ *
+ * So we wait for "fr_inv_done" to trigger
+ * and only put memory regions onto the drop_list
+ * that failed (i.e. not marked "FRMR_IS_FREE").
+ *
+ * This avoids the problem of memory-regions bouncing
+ * between "clean_list" and "drop_list" before they
+ * even have a chance to be properly invalidated.
+ */
+ frmr = &ibmr->u.frmr;
+ wait_event(frmr->fr_inv_done, frmr->fr_state != FRMR_IS_INUSE);
+ if (frmr->fr_state == FRMR_IS_FREE)
+ break;
rds_ib_free_frmr(ibmr, true);
+ }
ibmr = rds_ib_alloc_frmr(rds_ibdev, nents);
if (IS_ERR(ibmr))
return ibmr;
diff --git a/net/rds/ib_mr.h b/net/rds/ib_mr.h
index 5da12c248431..42daccb7b5eb 100644
--- a/net/rds/ib_mr.h
+++ b/net/rds/ib_mr.h
@@ -57,6 +57,7 @@ struct rds_ib_frmr {
struct ib_mr *mr;
enum rds_ib_fr_state fr_state;
bool fr_inv;
+ wait_queue_head_t fr_inv_done;
struct ib_send_wr fr_wr;
unsigned int dma_npages;
unsigned int sg_byte_len;
--
2.22.0
