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Message-ID: <53b401d7-934c-4937-ab83-6732af47668d@csgroup.eu>
Date: Fri, 23 Feb 2024 05:38:18 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Sean Anderson <sean.anderson@...ux.dev>, "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
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 ?
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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