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@xxxxxxxxx. 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@xxxxxxxxxxxxxxx >> Reported-by: Vladimir Oltean <vladimir.oltean@xxxxxxx> >> Closes: https://lore.kernel.org/all/20230323153935.nofnjucqjqnz34ej@skbuf/ >> Reported-by: Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx> >> Closes: https://lore.kernel.org/linux-arm-kernel/87wmsyvclu.fsf@xxxxxxxxxxxxxx/ >> Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxxx> >> Reviewed-by: Camelia Groza <camelia.groza@xxxxxxx> >> Tested-by: Vladimir Oltean <vladimir.oltean@xxxxxxx> >> >> --- >> >> 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 >>
