linux-kernel - Re: [PATCH v2] spmi: spmi-pmic-arb: fix irq_set

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Date:   Wed, 15 Dec 2021 23:14:01 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     David Collins <quic_collinsd@...cinc.com>,
        linux-kernel@...r.kernel.org
Cc:     David Collins <quic_collinsd@...cinc.com>,
        linux-arm-msm@...r.kernel.org,
        Kiran Gunda <quic_kgunda@...cinc.com>,
        Anirudh Ghayal <quic_aghayal@...cinc.com>,
        Subbaraman Narayanamurthy <quic_subbaram@...cinc.com>
Subject: Re: [PATCH v2] spmi: spmi-pmic-arb: fix irq_set_type race condition

Quoting David Collins (2021-11-17 19:47:19)
> 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
> enabled.
> 
> 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 holding the spmi-pmic-arb spinlock for
> the duration of the read, modify, write sequence performed in the
> qpnpint_irq_set_type() function.  Split the pmic_arb_read_cmd()
> and pmic_arb_write_cmd() functions each into three parts so that
> hardware register IO is decoupled from spinlock locking.  This
> allows a new function pmic_arb_masked_write() to be added which
> locks the spinlock and then calls register IO functions to
> perform SPMI read and write commands in a single atomic
> operation.
> 
> Signed-off-by: David Collins <quic_collinsd@...cinc.com>
> ---

Applied to spmi-next