When QMAN_FQ_FLAG_DYNAMIC_FQID is set, there's a race condition between
fq_table[fq->idx] state and freeing/allocating from the pool and
WARN_ON(fq_table[fq->idx]) in qman_create_fq() gets triggered.
Indeed, we can have:
Thread A Thread B
qman_destroy_fq() qman_create_fq()
qman_release_fqid()
qman_shutdown_fq()
gen_pool_free()
-- At this point, the fqid is available again --
qman_alloc_fqid()
-- so, we can get the just-freed fqid in thread B --
fq->fqid = fqid;
fq->idx = fqid * 2;
WARN_ON(fq_table[fq->idx]);
fq_table[fq->idx] = fq;
fq_table[fq->idx] = NULL;
And adding some logs between qman_release_fqid() and
fq_table[fq->idx] = NULL makes the WARN_ON() trigger a lot more.
To prevent that, ensure that fq_table[fq->idx] is set to NULL before
gen_pool_free() is called by using smp_wmb().
Fixes: c535e923bb97 ("soc/fsl: Introduce DPAA 1.x QMan device driver")
Signed-off-by: Richard Genoud <[email protected]>
---
drivers/soc/fsl/qbman/qman.c | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)
NB: I'm not 100% sure of the need of a barrier here, since even without
it, the WARN_ON() wasn't triggered any more.
diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
index 6b392b3ad4b1..39a3e7aab6ff 100644
--- a/drivers/soc/fsl/qbman/qman.c
+++ b/drivers/soc/fsl/qbman/qman.c
@@ -1827,6 +1827,8 @@ EXPORT_SYMBOL(qman_create_fq);
void qman_destroy_fq(struct qman_fq *fq)
{
+ int leaked;
+
/*
* We don't need to lock the FQ as it is a pre-condition that the FQ be
* quiesced. Instead, run some checks.
@@ -1834,11 +1836,29 @@ void qman_destroy_fq(struct qman_fq *fq)
switch (fq->state) {
case qman_fq_state_parked:
case qman_fq_state_oos:
- if (fq_isset(fq, QMAN_FQ_FLAG_DYNAMIC_FQID))
- qman_release_fqid(fq->fqid);
+ /*
+ * There's a race condition here on releasing the fqid,
+ * setting the fq_table to NULL, and freeing the fqid.
+ * To prevent it, this order should be respected:
+ */
+ if (fq_isset(fq, QMAN_FQ_FLAG_DYNAMIC_FQID)) {
+ leaked = qman_shutdown_fq(fq->fqid);
+ if (leaked)
+ pr_debug("FQID %d leaked\n", fq->fqid);
+ }
DPAA_ASSERT(fq_table[fq->idx]);
fq_table[fq->idx] = NULL;
+
+ if (fq_isset(fq, QMAN_FQ_FLAG_DYNAMIC_FQID) && !leaked) {
+ /*
+ * fq_table[fq->idx] should be set to null before
+ * freeing fq->fqid otherwise it could by allocated by
+ * qman_alloc_fqid() while still being !NULL
+ */
+ smp_wmb();
+ gen_pool_free(qm_fqalloc, fq->fqid | DPAA_GENALLOC_OFF,
1);
+ }
return;
default:
break;
base-commit: 9448598b22c50c8a5bb77a9103e2d49f134c9578
--
2.47.3
