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Message-ID: <34da1e7b-029e-410b-8735-a10d6d267e2b@linux.dev>
Date: Fri, 23 Feb 2024 11:02:50 -0500
From: Sean Anderson <sean.anderson@...ux.dev>
To: Christophe Leroy <christophe.leroy@...roup.eu>,
"David S . Miller" <davem@...emloft.net>, Eric Dumazet
<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc: Vladimir Oltean <vladimir.oltean@....com>, Roy Pledge
<roy.pledge@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"stable@...r.kernel.org" <stable@...r.kernel.org>,
Li Yang <leoyang.li@....com>, Scott Wood <oss@...error.net>,
Claudiu Manoil <claudiu.manoil@....com>,
Camelia Groza <camelia.groza@....com>,
Steffen Trumtrar <s.trumtrar@...gutronix.de>,
"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: 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 :
>> [Vous ne recevez pas souvent de courriers de sean.anderson@...ux.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@...r.kernel.org
>> Reported-by: Vladimir Oltean <vladimir.oltean@....com>
>> Closes: https://lore.kernel.org/all/20230323153935.nofnjucqjqnz34ej@skbuf/
>> Reported-by: Steffen Trumtrar <s.trumtrar@...gutronix.de>
>> Closes: https://lore.kernel.org/linux-arm-kernel/87wmsyvclu.fsf@pengutronix.de/
>> Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
>> Reviewed-by: Camelia Groza <camelia.groza@....com>
>> Tested-by: Vladimir Oltean <vladimir.oltean@....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
>>
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