Re: [RESEND2 PATCH net v4 2/2] soc: fsl: qbman: Use raw spinlock for cgr_lock

On 2/23/24 00:38, Christophe Leroy wrote:

Le 22/02/2024 à 18:07, Sean Anderson a écrit :

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cgr_lock may be locked with interrupts already disabled by smp_call_function_single. As such, we must use a raw spinlock to avoid problems on PREEMPT_RT kernels. Although this bug has existed for a while, it was not apparent until commit ef2a8d5478b9 ("net: dpaa: Adjust queue depth on rate change") which invokes smp_call_function_single via qman_update_cgr_safe every time a link goes up or down.

Why a raw spinlock to avoid problems on PREEMPT_RT, can you elaborate ?

smp_call_function always runs its callback in hard IRQ context, even on PREEMPT_RT, where spinlocks can sleep. So we need to use raw spinlocks to ensure we aren't waiting on a sleeping task. See the first bug report for more discussion.

In the longer term it would be better to switch to some other abstraction.

--Sean

If the problem is that interrupts are already disabled, shouldn't you just change the spin_lock_irq() by spin_lock_irqsave() ?

Christophe

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Fixes: 96f413f47677 ("soc/fsl/qbman: fix issue in qman_delete_cgr_safe()") CC: stable@vger.kernel.org Reported-by: Vladimir Oltean vladimir.oltean@nxp.com Closes: https://lore.kernel.org/all/20230323153935.nofnjucqjqnz34ej@skbuf/ Reported-by: Steffen Trumtrar s.trumtrar@pengutronix.de Closes: https://lore.kernel.org/linux-arm-kernel/87wmsyvclu.fsf@pengutronix.de/ Signed-off-by: Sean Anderson sean.anderson@linux.dev Reviewed-by: Camelia Groza camelia.groza@nxp.com Tested-by: Vladimir Oltean vladimir.oltean@nxp.com

---

Changes in v4:

• Add a note about how raw spinlocks aren't quite right

Changes in v3:

• Change blamed commit to something more appropriate

  drivers/soc/fsl/qbman/qman.c | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c index 1bf1f1ea67f0..7e9074519ad2 100644 --- a/drivers/soc/fsl/qbman/qman.c +++ b/drivers/soc/fsl/qbman/qman.c @@ -991,7 +991,7 @@ struct qman_portal { /* linked-list of CSCN handlers. */ struct list_head cgr_cbs; /* list lock */

•   spinlock_t cgr_lock;
  

•   raw_spinlock_t cgr_lock;
     struct work_struct congestion_work;
     struct work_struct mr_work;
     char irqname[MAX_IRQNAME];
  

@@ -1281,7 +1281,7 @@ static int qman_create_portal(struct qman_portal *portal, /* if the given mask is NULL, assume all CGRs can be seen */ qman_cgrs_fill(&portal->cgrs[0]); INIT_LIST_HEAD(&portal->cgr_cbs);

•   spin_lock_init(&portal->cgr_lock);
  

•   raw_spin_lock_init(&portal->cgr_lock);
     INIT_WORK(&portal->congestion_work, qm_congestion_task);
     INIT_WORK(&portal->mr_work, qm_mr_process_task);
     portal->bits = 0;
  

@@ -1456,11 +1456,14 @@ static void qm_congestion_task(struct work_struct *work) union qm_mc_result *mcr; struct qman_cgr *cgr;

•   spin_lock_irq(&p->cgr_lock);
  

•   /*
  

•    * FIXME: QM_MCR_TIMEOUT is 10ms, which is too long for a raw spinlock!
  

•    */
  

•   raw_spin_lock_irq(&p->cgr_lock);
     qm_mc_start(&p->p);
     qm_mc_commit(&p->p, QM_MCC_VERB_QUERYCONGESTION);
     if (!qm_mc_result_timeout(&p->p, &mcr)) {
  

•           spin_unlock_irq(&p->cgr_lock);
  

•           raw_spin_unlock_irq(&p->cgr_lock);
             dev_crit(p->config->dev, "QUERYCONGESTION timeout\n");
             qman_p_irqsource_add(p, QM_PIRQ_CSCI);
             return;
  

@@ -1476,7 +1479,7 @@ static void qm_congestion_task(struct work_struct *work) list_for_each_entry(cgr, &p->cgr_cbs, node) if (cgr->cb && qman_cgrs_get(&c, cgr->cgrid)) cgr->cb(p, cgr, qman_cgrs_get(&rr, cgr->cgrid));

•   spin_unlock_irq(&p->cgr_lock);
  

•   raw_spin_unlock_irq(&p->cgr_lock);
     qman_p_irqsource_add(p, QM_PIRQ_CSCI);
  

  }

@@ -2440,7 +2443,7 @@ int qman_create_cgr(struct qman_cgr *cgr, u32 flags, preempt_enable();

     cgr->chan = p->config->channel;

•   spin_lock_irq(&p->cgr_lock);
  

•   raw_spin_lock_irq(&p->cgr_lock);
  
     if (opts) {
             struct qm_mcc_initcgr local_opts = *opts;
  

@@ -2477,7 +2480,7 @@ int qman_create_cgr(struct qman_cgr *cgr, u32 flags, qman_cgrs_get(&p->cgrs[1], cgr->cgrid)) cgr->cb(p, cgr, 1); out:

•   spin_unlock_irq(&p->cgr_lock);
  

•   raw_spin_unlock_irq(&p->cgr_lock);
     put_affine_portal();
     return ret;
  

  }

@@ -2512,7 +2515,7 @@ int qman_delete_cgr(struct qman_cgr *cgr) return -EINVAL;

     memset(&local_opts, 0, sizeof(struct qm_mcc_initcgr));

•   spin_lock_irqsave(&p->cgr_lock, irqflags);
  

•   raw_spin_lock_irqsave(&p->cgr_lock, irqflags);
     list_del(&cgr->node);
     /*
      * If there are no other CGR objects for this CGRID in the list,
  

@@ -2537,7 +2540,7 @@ int qman_delete_cgr(struct qman_cgr *cgr) /* add back to the list */ list_add(&cgr->node, &p->cgr_cbs); release_lock:

•   spin_unlock_irqrestore(&p->cgr_lock, irqflags);
  

•   raw_spin_unlock_irqrestore(&p->cgr_lock, irqflags);
     put_affine_portal();
     return ret;
  

  }

@@ -2577,9 +2580,9 @@ static int qman_update_cgr(struct qman_cgr *cgr, struct qm_mcc_initcgr *opts) if (!p) return -EINVAL;

•   spin_lock_irqsave(&p->cgr_lock, irqflags);
  

•   raw_spin_lock_irqsave(&p->cgr_lock, irqflags);
     ret = qm_modify_cgr(cgr, 0, opts);
  

•   spin_unlock_irqrestore(&p->cgr_lock, irqflags);
  

•   raw_spin_unlock_irqrestore(&p->cgr_lock, irqflags);
     put_affine_portal();
     return ret;
  

  }

-- 2.35.1.1320.gc452695387.dirty