Re: [RESEND PATCH] spmi: spmi-pmic-arb: fix irq_set_type race condition

From: David Collins
Date: Mon Aug 02 2021 - 21:37:56 EST

On 7/31/21 1:20 AM, Stephen Boyd wrote:
+irqchip driver maintainers

Quoting David Collins (2021-07-28 11:02:09)
The qpnpint_irq_set_type() callback function configures the type
(edge vs level) and polarity (high, low, or both) of a particular
PMIC interrupt within a given peripheral. To do this, it reads
the three consecutive IRQ configuration registers, modifies the
specified IRQ bit within the register values, and finally writes
the three modified register values back to the PMIC. While a
spinlock is used to provide mutual exclusion on the SPMI bus
during the register read and write calls, there is no locking
around the overall read, modify, write sequence. This opens up
the possibility of a race condition if two tasks set the type of
a PMIC IRQ within the same peripheral simultaneously.

When the race condition is encountered, both tasks will read the
old value of the registers and IRQ bits set by one of the tasks
will be dropped upon the register write of the other task. This
then leads to PMIC IRQs being enabled with an incorrect type and
polarity configured. Such misconfiguration can lead to an IRQ
storm that overwhelms the system and causes it to crash.

This race condition and IRQ storm have been observed when using
a pair of pm8941-pwrkey devices to handle PMK8350 pwrkey and
resin interrupts. The independent devices probe asynchronously
in parallel and can simultaneously request and configure PMIC
IRQs in the same PMIC peripheral.

For a good case, the IRQ configuration calls end up serialized
due to timing deltas and the register read/write sequence looks
like this:

1. pwrkey probe: SPMI read(0x1311): 0x00, 0x00, 0x00
2. pwrkey probe: SPMI write(0x1311): 0x80, 0x80, 0x80
3. resin probe: SPMI read(0x1311): 0x80, 0x80, 0x80
4. resin probe: SPMI write(0x1311): 0xC0, 0xC0, 0xC0

The final register states after both devices have requested and
enabled their respective IRQs is thus:

0x1311: 0xC0
0x1312: 0xC0
0x1313: 0xC0
0x1314: 0x00
0x1315: 0xC0

For a bad case, the IRQ configuration calls end up occurring
simultaneously and the race condition is encountered. The
register read/write sequence then looks like this:

1. pwrkey probe: SPMI read(0x1311): 0x00, 0x00, 0x00
2. resin probe: SPMI read(0x1311): 0x00, 0x00, 0x00
3. pwrkey probe: SPMI write(0x1311): 0x80, 0x80, 0x80
4. resin probe: SPMI write(0x1311): 0x40, 0x40, 0x40

In this case, the final register states after both devices have
requested and enabled their respective IRQs is thus:

0x1311: 0x40
0x1312: 0x40
0x1313: 0x40
0x1314: 0x00
0x1315: 0xC0

This corresponds to the resin IRQ being configured for both
rising and falling edges, as expected. However, the pwrkey IRQ
is misconfigured as level type with both polarity high and low
set to disabled. The PMIC IRQ triggering hardware treats this
particular register configuration as if level low triggering is

The raw pwrkey IRQ signal is low when the power key is not being
pressed. Thus, the pwrkey IRQ begins firing continuously in an
IRQ storm.

Fix the race condition by locking a spinlock for the duration of
the read, modify, write sequence in the qpnpint_irq_set_type()

Fixes: 67b563f1f258 ("spmi: pmic_arb: add support for interrupt handling")
Signed-off-by: David Collins <collinsd@xxxxxxxxxxxxxx>
drivers/spmi/spmi-pmic-arb.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/spmi/spmi-pmic-arb.c b/drivers/spmi/spmi-pmic-arb.c
index bbbd311eda03..379ad6c1c14a 100644
--- a/drivers/spmi/spmi-pmic-arb.c
+++ b/drivers/spmi/spmi-pmic-arb.c
@@ -127,6 +127,7 @@ struct apid_data {
* @intr: address of the SPMI interrupt control registers.
* @cnfg: address of the PMIC Arbiter configuration registers.
* @lock: lock to synchronize accesses.
+ * @irq_lock: lock to ensure mutual exclusion for IRQ type setting
* @channel: execution environment channel to use for accesses.
* @irq: PMIC ARB interrupt.
* @ee: the current Execution Environment
@@ -146,6 +147,7 @@ struct spmi_pmic_arb {
void __iomem *core;
resource_size_t core_size;
raw_spinlock_t lock;
+ raw_spinlock_t irq_lock;

Maybe a better name is type_lock given that it's about the irq type
setting rmw sequence.

Sure, I'm ok with changing the name (assuming that the second lock is kept).

u8 channel;
int irq;
u8 ee;
@@ -600,10 +602,13 @@ static void qpnpint_irq_unmask(struct irq_data *d)
static int qpnpint_irq_set_type(struct irq_data *d, unsigned int flow_type)
+ struct spmi_pmic_arb *pmic_arb = irq_data_get_irq_chip_data(d);
struct spmi_pmic_arb_qpnpint_type type;
irq_flow_handler_t flow_handler;
u8 irq = hwirq_to_irq(d->hwirq);
+ unsigned long flags;
+ raw_spin_lock_irqsave(&pmic_arb->irq_lock, flags);
qpnpint_spmi_read(d, QPNPINT_REG_SET_TYPE, &type, sizeof(type));
@@ -616,8 +621,10 @@ static int qpnpint_irq_set_type(struct irq_data *d, unsigned int flow_type)
flow_handler = handle_edge_irq;
} else {
if ((flow_type & (IRQF_TRIGGER_HIGH)) &&
- (flow_type & (IRQF_TRIGGER_LOW)))
+ (flow_type & (IRQF_TRIGGER_LOW))) {
+ raw_spin_unlock_irqrestore(&pmic_arb->irq_lock, flags);
return -EINVAL;
+ }
type.type &= ~BIT(irq); /* level trig */
if (flow_type & IRQF_TRIGGER_HIGH)
@@ -629,6 +636,8 @@ static int qpnpint_irq_set_type(struct irq_data *d, unsigned int flow_type)
qpnpint_spmi_write(d, QPNPINT_REG_SET_TYPE, &type, sizeof(type));
+ raw_spin_unlock_irqrestore(&pmic_arb->irq_lock, flags);

Could we have a qpnpint_spmi_set_bit/clear_bit() API that takes the bit
we want to touch as an argument and then does it all under the originial
pmic_arb->lock? Then we don't need a different lock, we can avoid that
drop the lock under the else if condition above, and the area for the
lock will be contained within the set/clear function instead of here.

pmic_arb->lock is currently used tightly around the code in the SPMI bus callback functions which write to SPMI PMIC arbiter registers to trigger an SPMI transaction, poll in a loop to wait for completion, and read any command results. Each of these uses correspond to a command defined in the MIPI SPMI spec. There is no read-modify-write command in the spec.

Thus, implementing qpnpint_spmi_set_bit/clear_bit() functions would require an approach like one of these:

1. Removing the locking from pmic_arb_read_cmd() and pmic_arb_write_cmd(), defining new wrapper functions around them to just contain the locking, and adding a read-modify-write wrapper function that locks and calls both pmic_arb_read_cmd() and pmic_arb_write_cmd().

2. Or, create a new function that duplicates the contents of both pmic_arb_read_cmd() and pmic_arb_write_cmd(), allowing it to issue two SPMI bus commands with pmic_arb->lock held.

Option #1 seems like it would result in less clear and messy code than is currently present. It would also have a minor performance impact during simultaneous SPMI requests due to non-contentious checks, address look-ups and command formatting unnecessarily waiting for lock acquisition.

Option #2 would likely be less messy than option #1; however, it results in duplication of low-level code which is undesirable.

I prefer the approach used in this patch as it doesn't disrupt the architecture of the SPMI bus and PMIC IRQ functions. However, I'm willing to switch to your suggestion if you think it is a better design and cleaner/clearer solution. Please let me know your thoughts. Would you want option #1, #2, or something else?

irq_set_handler_locked(d, flow_handler);
return 0;
@@ -1285,6 +1294,7 @@ static int spmi_pmic_arb_probe(struct platform_device *pdev)
platform_set_drvdata(pdev, ctrl);
+ raw_spin_lock_init(&pmic_arb->irq_lock);
ctrl->cmd = pmic_arb_cmd;
ctrl->read_cmd = pmic_arb_read_cmd;


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