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: [email protected]
Signed-off-by: Sean Anderson <[email protected]>
Reviewed-by: Camelia Groza <[email protected]>
Tested-by: Vladimir Oltean <[email protected]>
---
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
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: [email protected]
Reported-by: Vladimir Oltean <[email protected]>
Closes: https://lore.kernel.org/all/20230323153935.nofnjucqjqnz34ej@skbuf/
Reported-by: Steffen Trumtrar <[email protected]>
Closes: https://lore.kernel.org/linux-arm-kernel/[email protected]/
Signed-off-by: Sean Anderson <[email protected]>
Reviewed-by: Camelia Groza <[email protected]>
Tested-by: Vladimir Oltean <[email protected]>
---
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
Le 22/02/2024 à 18:07, Sean Anderson a écrit :
> [Vous ne recevez pas souvent de courriers de [email protected]. 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: [email protected]
> Reported-by: Vladimir Oltean <[email protected]>
> Closes: https://lore.kernel.org/all/20230323153935.nofnjucqjqnz34ej@skbuf/
> Reported-by: Steffen Trumtrar <[email protected]>
> Closes: https://lore.kernel.org/linux-arm-kernel/[email protected]/
> Signed-off-by: Sean Anderson <[email protected]>
> Reviewed-by: Camelia Groza <[email protected]>
> Tested-by: Vladimir Oltean <[email protected]>
>
> ---
>
> 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
>
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 [email protected]. 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: [email protected]
>> Reported-by: Vladimir Oltean <[email protected]>
>> Closes: https://lore.kernel.org/all/20230323153935.nofnjucqjqnz34ej@skbuf/
>> Reported-by: Steffen Trumtrar <[email protected]>
>> Closes: https://lore.kernel.org/linux-arm-kernel/[email protected]/
>> Signed-off-by: Sean Anderson <[email protected]>
>> Reviewed-by: Camelia Groza <[email protected]>
>> Tested-by: Vladimir Oltean <[email protected]>
>>
>> ---
>>
>> 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
>>
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 [email protected]. 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
Le 05/03/2024 à 19:14, Sean Anderson a écrit :
> [Vous ne recevez pas souvent de courriers de [email protected]. 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 [email protected]. 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
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 [email protected]. 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 [email protected]. 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