[RESEND2 PATCH net v4 1/2] soc: fsl: qbman: Always disable interrupts when taking cgr_lock

[RESEND2 PATCH net v4 1/2] soc: fsl: qbman: Always disable interrupts when taking cgr_lock

[Sean Anderson]

smp_call_function_single disables IRQs when executing the callback. To
prevent deadlocks, we must disable IRQs when taking cgr_lock elsewhere.
This is already done by qman_update_cgr and qman_delete_cgr; fix the
other lockers.

Fixes: 96f413f47677 ("soc/fsl/qbman: fix issue in qman_delete_cgr_safe()")
CC: stable@vger.kernel.org
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>
---
Resent from a non-mangling email.

(no changes since v3)

Changes in v3:
- Change blamed commit to something more appropriate

Changes in v2:
- Fix one additional call to spin_unlock

 drivers/soc/fsl/qbman/qman.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
index 739e4eee6b75..1bf1f1ea67f0 100644
--- a/drivers/soc/fsl/qbman/qman.c
+++ b/drivers/soc/fsl/qbman/qman.c
@@ -1456,11 +1456,11 @@ static void qm_congestion_task(struct work_struct *work)
 	union qm_mc_result *mcr;
 	struct qman_cgr *cgr;
 
-	spin_lock(&p->cgr_lock);
+	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(&p->cgr_lock);
+		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 +1476,7 @@ 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(&p->cgr_lock);
+	spin_unlock_irq(&p->cgr_lock);
 	qman_p_irqsource_add(p, QM_PIRQ_CSCI);
 }
 
@@ -2440,7 +2440,7 @@ int qman_create_cgr(struct qman_cgr *cgr, u32 flags,
 	preempt_enable();
 
 	cgr->chan = p->config->channel;
-	spin_lock(&p->cgr_lock);
+	spin_lock_irq(&p->cgr_lock);
 
 	if (opts) {
 		struct qm_mcc_initcgr local_opts = *opts;
@@ -2477,7 +2477,7 @@ 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(&p->cgr_lock);
+	spin_unlock_irq(&p->cgr_lock);
 	put_affine_portal();
 	return ret;
 }
-- 
2.35.1.1320.gc452695387.dirty

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

[Sean Anderson]

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.

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

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

[Christophe Leroy]

Le 22/02/2024 à 18:07, Sean Anderson a écrit :
> [Vous ne recevez pas souvent de courriers de sean.anderson@linux.dev. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> 
> 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 ?

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

Christophe


> 
> 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
> 

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

[Sean Anderson]

On 2/23/24 00:38, Christophe Leroy wrote:
> Le 22/02/2024 à 18:07, Sean Anderson a écrit :
>> [Vous ne recevez pas souvent de courriers de sean.anderson@linux.dev. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
>> 
>> 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
> 
> 
>> 
>> 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
>> 

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

[Sean Anderson]

Hi,

On 2/23/24 11:02, Sean Anderson wrote:
> On 2/23/24 00:38, Christophe Leroy wrote:
>> Le 22/02/2024 à 18:07, Sean Anderson a écrit :
>>> [Vous ne recevez pas souvent de courriers de sean.anderson@linux.dev. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
>>> 
>>> 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.

Does this make sense to you?

--Sean

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

[Christophe Leroy]

Le 05/03/2024 à 19:14, Sean Anderson a écrit :
> [Vous ne recevez pas souvent de courriers de sean.anderson@linux.dev. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> 
> Hi,
> 
> On 2/23/24 11:02, Sean Anderson wrote:
>> On 2/23/24 00:38, Christophe Leroy wrote:
>>> Le 22/02/2024 à 18:07, Sean Anderson a écrit :
>>>> [Vous ne recevez pas souvent de courriers de sean.anderson@linux.dev. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
>>>>
>>>> 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.
> 
> Does this make sense to you?

Yes that fine, thanks for the clarification. Maybe you can explain that 
in the patch description in case you send a v5.

Christophe

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

[Sean Anderson]

On 3/5/24 17:18, Christophe Leroy wrote:
> 
> 
> Le 05/03/2024 à 19:14, Sean Anderson a écrit :
>> [Vous ne recevez pas souvent de courriers de sean.anderson@linux.dev. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
>> 
>> Hi,
>> 
>> On 2/23/24 11:02, Sean Anderson wrote:
>>> On 2/23/24 00:38, Christophe Leroy wrote:
>>>> Le 22/02/2024 à 18:07, Sean Anderson a écrit :
>>>>> [Vous ne recevez pas souvent de courriers de sean.anderson@linux.dev. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
>>>>>
>>>>> 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.
>> 
>> Does this make sense to you?
> 
> Yes that fine, thanks for the clarification. Maybe you can explain that 
> in the patch description in case you send a v5.

Hm, I thought I put this description in the commit message already.
Maybe something like

| smp_call_function always runs its callback in hard IRQ context, even on
| PREEMPT_RT, where spinlocks can sleep. So we need to use a raw spinlock
| for cgr_lock to ensure we aren't waiting on a sleeping task.
| 
| 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.

would be clearer.

--Sean