[PATCH 5.10 198/491] soc: fsl: qbman: fix race condition in qman_destroy_fq

Greg Kroah-Hartman
2026-04-13T16:51:10Z

From: Richard Genoud <richard.genoud@bootlin.com>

[ Upstream commit 014077044e874e270ec480515edbc1cadb976cf2 ]

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 <richard.genoud@bootlin.com>
Tested-by: CHAMPSEIX Thomas <thomas.champseix@alstomgroup.com>
Link: https://lore.kernel.org/r/20251223072549.397625-1-richard.genoud@bootlin.com
Signed-off-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/soc/fsl/qbman/qman.c | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
index 7abc9b6a04ab6..0309ed2df0d71 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;
--
2.51.0