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From:   Jason Liu <jason.hui.liu@nxp.com>
To:     Sudeep Holla <sudeep.holla@arm.com>, Marc Zyngier <maz@kernel.org>
CC:     "catalin.marinas@arm.com" <catalin.marinas@arm.com>,
        "will@kernel.org" <will@kernel.org>,
        "sashal@kernel.org" <sashal@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>
Subject: RE: [PATCH 1/1] arm64: kexec: no need to do irq_chip->irq_mask if it
 already masked
Thread-Topic: [PATCH 1/1] arm64: kexec: no need to do irq_chip->irq_mask if it
 already masked
Thread-Index: AQHWaj3ZMAA/XWH8SkmG3qCWNnZEoaknx/iAgAALMQCAAQxYoA==
Date:   Wed, 5 Aug 2020 06:31:20 +0000
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References: <20200804085657.10776-1-jason.hui.liu@nxp.com>
 <b4444c737f9d6fd8fd99dbb809d35a0f@kernel.org> <20200804113850.GB15199@bogus>
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> -----Original Message-----
> From: Sudeep Holla <sudeep.holla@arm.com>
> Sent: Tuesday, August 4, 2020 7:39 PM
> To: Marc Zyngier <maz@kernel.org>
> Cc: Jason Liu <jason.hui.liu@nxp.com>; catalin.marinas@arm.com;
> will@kernel.org; linux-kernel@vger.kernel.org; Sudeep Holla
> <sudeep.holla@arm.com>; linux-arm-kernel@lists.infradead.org
> Subject: Re: [PATCH 1/1] arm64: kexec: no need to do irq_chip->irq_mask i=
f it
> already masked
>=20
> On Tue, Aug 04, 2020 at 11:58:47AM +0100, Marc Zyngier wrote:
> > On 2020-08-04 09:56, Jason Liu wrote:
> > > No need to do the irq_chip->irq_mask() if it already masked.
> > > BTW, unconditionally do the irq_chip->irq_mask() will also bring
> > > issues when the irq_chip in the runtime PM suspend. Accessing
> > > registers of the irq_chip will bring in the exceptions. For example o=
n the
> i.MX:
> > >
> > > root@imx8qmmek:~# echo c > /proc/sysrq-trigger [  177.796182] sysrq:
> > > Trigger a crash [  177.799596] Kernel panic - not syncing: sysrq
> > > triggered crash [  177.875616] SMP: stopping secondary CPUs [
> > > 177.891936] Internal error: synchronous external abort: 96000210
> > > [#1] PREEMPT SMP [  177.899429] Modules linked in: crct10dif_ce
> > > mxc_jpeg_encdec [  177.905018] CPU: 1 PID: 944 Comm: sh Kdump:
> > > loaded Not tainted [  177.913457] Hardware name: Freescale i.MX8QM
> > > MEK (DT) [  177.918517] pstate: a0000085 (NzCv daIf -PAN -UAO) [
> > > 177.923318] pc : imx_irqsteer_irq_mask+0x50/0x80 [  177.927944] lr :
> > > imx_irqsteer_irq_mask+0x38/0x80 [  177.932561] sp : ffff800011fe3a50
> > > [  177.935880] x29: ffff800011fe3a50 x28: ffff0008f7708e00 [
> > > 177.941196] x27: 0000000000000000 x26: 0000000000000000 [
> > > 177.946513] x25: ffff800011a30c80 x24: 0000000000000000 [
> > > 177.951830] x23: ffff800011fe3af8 x22: ffff0008f24469d4 [
> > > 177.957147] x21: ffff0008f2446880 x20: ffff0008f25f5658 [
> > > 177.962463] x19: ffff800012611004 x18: 0000000000000001 [
> > > 177.967780] x17: 0000000000000000 x16: 0000000000000000 [
> > > 177.973097] x15: ffff0008f7709270 x14: 0000000060000085 [
> > > 177.978414] x13: ffff800010177570 x12: ffff800011fe3ab0 [
> > > 177.983730] x11: ffff80001017749c x10: 0000000000000040 [
> > > 177.989047] x9 : ffff8000119f1c80 x8 : ffff8000119f1c78 [
> > > 177.994364] x7 : ffff0008f46bedf8 x6 : 0000000000000000 [
> > > 177.999681] x5 : ffff0008f46beda0 x4 : 0000000000000000 [
> > > 178.004997] x3 : ffff0008f24469d4 x2 : ffff800012611000 [
> > > 178.010314] x1 : 0000000000000080 x0 : 0000000000000080 [
> > > 178.015630] Call trace:
> > > [  178.018077]  imx_irqsteer_irq_mask+0x50/0x80 [  178.022352]
> > > machine_crash_shutdown+0xa8/0x100 [  178.026802]
> > > __crash_kexec+0x6c/0x118 [  178.030464]  panic+0x19c/0x324 [
> > > 178.033524]  sysrq_handle_reboot+0x0/0x20 [  178.037537]
> > > __handle_sysrq+0x88/0x180 [  178.041290]
> > > write_sysrq_trigger+0x8c/0xb0 [  178.045389]
> > > proc_reg_write+0x78/0xb0 [  178.049055]  __vfs_write+0x18/0x40 [
> > > 178.052461]  vfs_write+0xdc/0x1c8 [  178.055779]
> > > ksys_write+0x68/0xf0 [  178.059098]  __arm64_sys_write+0x18/0x20 [
> > > 178.063027]  el0_svc_common.constprop.0+0x68/0x160
> > > [  178.067821]  el0_svc_handler+0x20/0x80 [  178.071573]
> > > el0_svc+0x8/0xc [  178.074463] Code: 93407e73 91001273 aa0003e1
> > > 8b130053 (b9400260) [  178.080567] ---[ end trace 652333f6c6d6b05d
> > > ]---
> > >
> > > Signed-off-by: Jason Liu <jason.hui.liu@nxp.com>
> > > Cc: <stable@vger.kernel.org>
> > > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > > Cc: Will Deacon <will@kernel.org>
> > > Cc: Sasha Levin <sashal@kernel.org>
> > > ---
> > >  arch/arm64/kernel/machine_kexec.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/arch/arm64/kernel/machine_kexec.c
> > > b/arch/arm64/kernel/machine_kexec.c
> > > index a0b144cfaea7..8ab263c733bf 100644
> > > --- a/arch/arm64/kernel/machine_kexec.c
> > > +++ b/arch/arm64/kernel/machine_kexec.c
> > > @@ -236,7 +236,7 @@ static void machine_kexec_mask_interrupts(void)
> > >  		    chip->irq_eoi)
> > >  			chip->irq_eoi(&desc->irq_data);
> > >
> > > -		if (chip->irq_mask)
> > > +		if (chip->irq_mask && !irqd_irq_masked(&desc->irq_data))
> > >  			chip->irq_mask(&desc->irq_data);
> > >
> > >  		if (chip->irq_disable && !irqd_irq_disabled(&desc->irq_data))
> >
> > This is pretty dodgy. irq_mask() should be an idempotent action
> > (masking twice must not be harmful).
> >
>=20
> That was my understanding too, but was not totally against adding it here=
.

Yes, masking twice at least a time of waste and really no need to do it. If=
 you look at the common API mask_irq
There did avoid the unnecessary twice or multiple mask. Keep in mind that t=
here are many irqs, so it will
waste time to do the things which is not necessary. So, from this point, IM=
O, this patch is fine.

void mask_irq(struct irq_desc *desc)
{
        if (irqd_irq_masked(&desc->irq_data))
                return;

        if (desc->irq_data.chip->irq_mask) {
                desc->irq_data.chip->irq_mask(&desc->irq_data);
                irq_state_set_masked(desc);
        }
}

>=20
> > Even more, it really isn't obvious to me how this can work at all, as
> > even if the interrupt isn't masked, the irqsteer could well be
> > suspended.
> >
>=20
> Indeed, the runtime PM ops in that driver looks dodgy. Any calls to mask_=
irq
> from drivers or anywhere with irqchip suspended with just blows up the
> system.

If you look at the chip->irq_mask implementation on different platforms, al=
most
all with directly access the register of the irqchip including irqsteer. Th=
ere are fine due to
driver will use the common mask_irq API.

>=20
> > So as is, this change is just papering over a much deeper issue in
> > your driver.
> >
>=20
> Thanks for confirming

No, this patch is not papering over a much deeper issue in the driver. This=
 is just to make things better for the ARM64 kexec.

>=20
> --
> Regards,
> Sudeep