[1/1] arm64: kexec: no need to do irq_chip->irq_mask if it already masked
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Message ID 20200804085657.10776-1-jason.hui.liu@nxp.com
State New
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Series
  • [1/1] arm64: kexec: no need to do irq_chip->irq_mask if it already masked
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Commit Message

Jason Liu Aug. 4, 2020, 8:56 a.m. UTC
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 on 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(-)

Comments

Sudeep Holla Aug. 4, 2020, 10:20 a.m. UTC | #1
+Marc Z

On Tue, Aug 04, 2020 at 04:56:57PM +0800, 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 on the i.MX:
>

The change looks good and is inline with the additional checks we do for
eoi and disable. However, the imx_irqsteer_irq_mask is not safe to be
called with runtime suspend. What happens if some driver using the irq
on this chip calls disable_irq when this irqchip is suspended ?
Marc Zyngier Aug. 4, 2020, 10:58 a.m. UTC | #2
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 on 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).

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.

So as is, this change is just papering over a much deeper issue
in your driver.

         M.
Sudeep Holla Aug. 4, 2020, 11:38 a.m. UTC | #3
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 on 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).
>

That was my understanding too, but was not totally against adding
it here.

> 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.
>

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.

> So as is, this change is just papering over a much deeper issue
> in your driver.
>

Thanks for confirming

--
Regards,
Sudeep
Jason Liu Aug. 5, 2020, 6:30 a.m. UTC | #4
> -----Original Message-----
> From: Sudeep Holla <sudeep.holla@arm.com>
> Sent: Tuesday, August 4, 2020 6:20 PM
> To: Jason Liu <jason.hui.liu@nxp.com>
> Cc: will@kernel.org; catalin.marinas@arm.com; ashal@kernel.org;
> maz@kernel.org; linux-arm-kernel@lists.infradead.org;
> linux-kernel@vger.kernel.org
> Subject: Re: [PATCH 1/1] arm64: kexec: no need to do irq_chip->irq_mask if it
> already masked
> 
> +Marc Z
> 
> On Tue, Aug 04, 2020 at 04:56:57PM +0800, 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 on the i.MX:
> >
> 
> The change looks good and is inline with the additional checks we do for eoi
> and disable. However, the imx_irqsteer_irq_mask is not safe to be called with
> runtime suspend. 

Yes, you are right. imx_irqsteer_irq_mask can not be called with irqchip runtime suspend.
IMO, this might apply to all platforms which implement the irq_chip->mask function with
directly access the registers.

> What happens if some driver using the irq on this chip calls
> disable_irq when this irqchip is suspended ?

IMO, only free_irq will call the irq_chip_pm_put which will bring the irqchip to suspend if that irq is the last user.
Otherwise, the irqchip is in active state. free_irq will set the IRQ state to DISABLED and MASKED.
So, if the irqchip in suspend state, which means all the irqs(associated with irqchip) were DISABLED and MASKED.
If call the common API disable_irq, that is fine due to the disable_irq will nop if the irq was DISABLED and masked. 

> 
> --
> Regards,
> Sudeep
Jason Liu Aug. 5, 2020, 6:31 a.m. UTC | #5
> -----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 if it
> already masked
> 
> 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 on 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).
> >
> 
> 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 there are many irqs, so it will
waste time to do the things which is not necessary. So, from this point, IMO, 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);
        }
}

> 
> > 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.
> >
> 
> 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, almost
all with directly access the register of the irqchip including irqsteer. There are fine due to
driver will use the common mask_irq API.

> 
> > So as is, this change is just papering over a much deeper issue in
> > your driver.
> >
> 
> 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.

> 
> --
> Regards,
> Sudeep
Marc Zyngier Aug. 5, 2020, 8:17 a.m. UTC | #6
On 2020-08-05 07:31, Jason Liu wrote:
>> -----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 if it
>> already masked
>> 
>> 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 on 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).
>> >
>> 
>> 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 there are many irqs, so it will
> waste time to do the things which is not necessary. So, from this
> point, IMO, this patch is fine.

Let's be serious. You are doing a *kexec*. Rebooting the entire system.
Another 10 or 1000 accesses are completely invisible here.

> 
> 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);
>         }
> }
> 
>> 
>> > 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.
>> >
>> 
>> 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, almost
> all with directly access the register of the irqchip including
> irqsteer. There are fine due to
> driver will use the common mask_irq API.
> 
>> 
>> > So as is, this change is just papering over a much deeper issue in
>> > your driver.
>> >
>> 
>> 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.

Yes, I'm sure it is... However:

request_irq()
<goes into suspend, panic somewhere after having turned the irqchip 
clock off>
if (chip->irq_mask && !irqd_irq_masked(&desc->irq_data))
     <explodes, as the interrupt isn't masked>

This is because the PM in the irqsteer driver is completely busted:
request_irq() should get a reference on the driver to prevent it
from being suspended. Since you don't implement it correctly, this
doesn't happen and your "improvement" doesn't help at all.

         M.
Sudeep Holla Aug. 5, 2020, 8:47 a.m. UTC | #7
On Wed, Aug 05, 2020 at 06:31:20AM +0000, Jason Liu wrote:
> >
> > 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, almost
> all with directly access the register of the irqchip including irqsteer.
> There are fine due to driver will use the common mask_irq API.
>

That still doesn't explain how you can prevent system from blowing up if
chip->irq_mask gets called with irqchip suspended ?

--
Regards,
Sudeep
Jason Liu Aug. 6, 2020, 10:05 a.m. UTC | #8
> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Wednesday, August 5, 2020 4:18 PM
> To: Jason Liu <jason.hui.liu@nxp.com>
> Cc: Sudeep Holla <sudeep.holla@arm.com>; catalin.marinas@arm.com;
> will@kernel.org; sashal@kernel.org; linux-kernel@vger.kernel.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
> 
> On 2020-08-05 07:31, Jason Liu wrote:
> >> -----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 if it already masked
> >>
> >> 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 on 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).
> >> >
> >>
> >> 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 there are many
> > irqs, so it will waste time to do the things which is not necessary.
> > So, from this point, IMO, this patch is fine.
> 
> Let's be serious. You are doing a *kexec*. Rebooting the entire system.
> Another 10 or 1000 accesses are completely invisible here.
> 
> >
> > 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);
> >         }
> > }
> >
> >>
> >> > 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.
> >> >
> >>
> >> 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, almost all with directly access the register of the irqchip
> > including irqsteer. There are fine due to driver will use the common
> > mask_irq API.
> >
> >>
> >> > So as is, this change is just papering over a much deeper issue in
> >> > your driver.
> >> >
> >>
> >> 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.
> 
> Yes, I'm sure it is... However:
> 
> request_irq()
> <goes into suspend, panic somewhere after having turned the irqchip clock off>
> if (chip->irq_mask && !irqd_irq_masked(&desc->irq_data))
>      <explodes, as the interrupt isn't masked>
> 
> This is because the PM in the irqsteer driver is completely busted:
> request_irq() should get a reference on the driver to prevent it from being
> suspended. Since you don't implement it correctly, this doesn't happen and
> your "improvement" doesn't help at all.

The request_irq will get a reference to prevent the irqchip from being suspended due to it call
irq_chip_pm_get(). I am pretty sure we have implemented correctly and that is also the common Linux code.
In order to save power and let the irqchip enter into runtime SUSPEND mode, the driver will call free_irq()
When it was not used(idle). Then free_irq() will decrease the reference and let the irqchip enter suspend state.

So, when the irqchip entered suspend, which means there is no user for the irqchip and all the irqs were DISABLED + MASKED.
Due to the runtimePM support for the irqchip, when kexec runs, it will sometimes meet the situation that the irqchip is suspend due to
no users for it. So from either the performance(time cost) or coding logic, the machine_kexec_mask_interrupts() should not do
double mask for the irqs which already masked.

> 
>          M.
> --
> Jazz is not dead. It just smells funny...
Jason Liu Aug. 6, 2020, 10:09 a.m. UTC | #9
> -----Original Message-----
> From: Sudeep Holla <sudeep.holla@arm.com>
> Sent: Wednesday, August 5, 2020 4:48 PM
> To: Jason Liu <jason.hui.liu@nxp.com>
> Cc: Marc Zyngier <maz@kernel.org>; catalin.marinas@arm.com;
> will@kernel.org; sashal@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 if it
> already masked
> 
> On Wed, Aug 05, 2020 at 06:31:20AM +0000, Jason Liu wrote:
> > >
> > > 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, almost all with directly access the register of the irqchip including
> irqsteer.
> > There are fine due to driver will use the common mask_irq API.
> >
> 
> That still doesn't explain how you can prevent system from blowing up if
> chip->irq_mask gets called with irqchip suspended ?

Do you mean driver, the driver will not call chip->irq_mask when irqchip was in suspend.
if it does, it will be big BUG. I believe we don't do that in the driver.

> 
> --
> Regards,
> Sudeep
Marc Zyngier Aug. 6, 2020, 12:25 p.m. UTC | #10
On 2020-08-06 11:05, Jason Liu wrote:
>> -----Original Message-----
>> From: Marc Zyngier <maz@kernel.org>

[...]

>> > 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.
>> 
>> Yes, I'm sure it is... However:
>> 
>> request_irq()
>> <goes into suspend, panic somewhere after having turned the irqchip 
>> clock off>
>> if (chip->irq_mask && !irqd_irq_masked(&desc->irq_data))
>>      <explodes, as the interrupt isn't masked>
>> 
>> This is because the PM in the irqsteer driver is completely busted:
>> request_irq() should get a reference on the driver to prevent it from 
>> being
>> suspended. Since you don't implement it correctly, this doesn't happen 
>> and
>> your "improvement" doesn't help at all.
> 
> The request_irq will get a reference to prevent the irqchip from being
> suspended due to it call
> irq_chip_pm_get(). I am pretty sure we have implemented correctly and
> that is also the common Linux code.

Then it seems you cannot read your own driver. At no point do you
set the parent_device that would give you a fighting chance to
get the device clocked and powered on. How does it work? Magic?

> In order to save power and let the irqchip enter into runtime SUSPEND
> mode, the driver will call free_irq()
> When it was not used(idle). Then free_irq() will decrease the
> reference and let the irqchip enter suspend state.

The reference count on *what*? There is nothing to take a reference
on. So yes, you understand how the core kernel works. But you don't
seem to notice that there is no link between the irq and the device
that implements the controller.

> So, when the irqchip entered suspend, which means there is no user for
> the irqchip and all the irqs were DISABLED + MASKED.
> Due to the runtimePM support for the irqchip, when kexec runs, it will
> sometimes meet the situation that the irqchip is suspend due to
> no users for it. So from either the performance(time cost) or coding
> logic, the machine_kexec_mask_interrupts() should not do
> double mask for the irqs which already masked.

I strongly suggest you start by fixing the damn driver first.

In the meantime, NAK to this patch.

         M.
Jason Liu Aug. 13, 2020, 6:03 a.m. UTC | #11
> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Thursday, August 6, 2020 8:26 PM
> To: Jason Liu <jason.hui.liu@nxp.com>
> Cc: Sudeep Holla <sudeep.holla@arm.com>; catalin.marinas@arm.com;
> will@kernel.org; sashal@kernel.org; linux-kernel@vger.kernel.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
> 
> On 2020-08-06 11:05, Jason Liu wrote:
> >> -----Original Message-----
> >> From: Marc Zyngier <maz@kernel.org>
> 
> [...]
> 
> >> > 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.
> >>
> >> Yes, I'm sure it is... However:
> >>
> >> request_irq()
> >> <goes into suspend, panic somewhere after having turned the irqchip
> >> clock off> if (chip->irq_mask && !irqd_irq_masked(&desc->irq_data))
> >>      <explodes, as the interrupt isn't masked>
> >>
> >> This is because the PM in the irqsteer driver is completely busted:
> >> request_irq() should get a reference on the driver to prevent it from
> >> being suspended. Since you don't implement it correctly, this doesn't
> >> happen and your "improvement" doesn't help at all.
> >
> > The request_irq will get a reference to prevent the irqchip from being
> > suspended due to it call irq_chip_pm_get(). I am pretty sure we have
> > implemented correctly and that is also the common Linux code.
> 
> Then it seems you cannot read your own driver. At no point do you set the
> parent_device that would give you a fighting chance to get the device clocked
> and powered on. How does it work? Magic?
> 
> > In order to save power and let the irqchip enter into runtime SUSPEND
> > mode, the driver will call free_irq() When it was not used(idle). Then
> > free_irq() will decrease the reference and let the irqchip enter
> > suspend state.
> 
> The reference count on *what*? There is nothing to take a reference on. So yes,
> you understand how the core kernel works. But you don't seem to notice that
> there is no link between the irq and the device that implements the controller.

See the code, it will call irq_chip_pm_put(&desc->irq_data)

/*
 * Internal function to unregister an irqaction - used to free
 * regular and special interrupts that are part of the architecture.
 */
static struct irqaction *__free_irq(struct irq_desc *desc, void *dev_id)
{
..
        irq_chip_pm_put(&desc->irq_data);
        module_put(desc->owner);
        kfree(action->secondary);
        return action;
}

> 
> > So, when the irqchip entered suspend, which means there is no user for
> > the irqchip and all the irqs were DISABLED + MASKED.
> > Due to the runtimePM support for the irqchip, when kexec runs, it will
> > sometimes meet the situation that the irqchip is suspend due to no
> > users for it. So from either the performance(time cost) or coding
> > logic, the machine_kexec_mask_interrupts() should not do double mask
> > for the irqs which already masked.
> 
> I strongly suggest you start by fixing the damn driver first.

Our driver does not have issue at all. What to fix?

> 
> In the meantime, NAK to this patch.

Anyway, it seems don't really understand this issue and you just simply reject one reasonable fix. Sounds not good at all.

> 
>          M.
> --
> Jazz is not dead. It just smells funny...
Marc Zyngier Aug. 13, 2020, 10:08 a.m. UTC | #12
On 2020-08-13 07:03, Jason Liu wrote:
>> -----Original Message-----
>> From: Marc Zyngier <maz@kernel.org>
>> Sent: Thursday, August 6, 2020 8:26 PM
>> To: Jason Liu <jason.hui.liu@nxp.com>
>> Cc: Sudeep Holla <sudeep.holla@arm.com>; catalin.marinas@arm.com;
>> will@kernel.org; sashal@kernel.org; linux-kernel@vger.kernel.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
>> 
>> On 2020-08-06 11:05, Jason Liu wrote:
>> >> -----Original Message-----
>> >> From: Marc Zyngier <maz@kernel.org>
>> 
>> [...]
>> 
>> >> > 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.
>> >>
>> >> Yes, I'm sure it is... However:
>> >>
>> >> request_irq()
>> >> <goes into suspend, panic somewhere after having turned the irqchip
>> >> clock off> if (chip->irq_mask && !irqd_irq_masked(&desc->irq_data))
>> >>      <explodes, as the interrupt isn't masked>
>> >>
>> >> This is because the PM in the irqsteer driver is completely busted:
>> >> request_irq() should get a reference on the driver to prevent it from
>> >> being suspended. Since you don't implement it correctly, this doesn't
>> >> happen and your "improvement" doesn't help at all.
>> >
>> > The request_irq will get a reference to prevent the irqchip from being
>> > suspended due to it call irq_chip_pm_get(). I am pretty sure we have
>> > implemented correctly and that is also the common Linux code.
>> 
>> Then it seems you cannot read your own driver. At no point do you set 
>> the
>> parent_device that would give you a fighting chance to get the device 
>> clocked
>> and powered on. How does it work? Magic?
>> 
>> > In order to save power and let the irqchip enter into runtime SUSPEND
>> > mode, the driver will call free_irq() When it was not used(idle). Then
>> > free_irq() will decrease the reference and let the irqchip enter
>> > suspend state.
>> 
>> The reference count on *what*? There is nothing to take a reference 
>> on. So yes,
>> you understand how the core kernel works. But you don't seem to notice 
>> that
>> there is no link between the irq and the device that implements the 
>> controller.
> 
> See the code, it will call irq_chip_pm_put(&desc->irq_data)
> 
> /*
>  * Internal function to unregister an irqaction - used to free
>  * regular and special interrupts that are part of the architecture.
>  */
> static struct irqaction *__free_irq(struct irq_desc *desc, void 
> *dev_id)
> {
> ..
>         irq_chip_pm_put(&desc->irq_data);
>         module_put(desc->owner);
>         kfree(action->secondary);
>         return action;
> }

This is getting tiresome. You want to play the code-quote game?

int irq_chip_pm_put(struct irq_data *data)
{
	int retval = 0;

	if (IS_ENABLED(CONFIG_PM) && data->chip->parent_device)
		retval = pm_runtime_put(data->chip->parent_device);

	return (retval < 0) ? retval : 0;
}

What is parent_device set to in your driver? Oh wait... Nothing.
So what does the code you quoted do? Not much.

>> > So, when the irqchip entered suspend, which means there is no user for
>> > the irqchip and all the irqs were DISABLED + MASKED.
>> > Due to the runtimePM support for the irqchip, when kexec runs, it will
>> > sometimes meet the situation that the irqchip is suspend due to no
>> > users for it. So from either the performance(time cost) or coding
>> > logic, the machine_kexec_mask_interrupts() should not do double mask
>> > for the irqs which already masked.
>> 
>> I strongly suggest you start by fixing the damn driver first.
> 
> Our driver does not have issue at all. What to fix?

[I've censored myself here...]

> 
>> 
>> In the meantime, NAK to this patch.
> 
> Anyway, it seems don't really understand this issue and you just
> simply reject one reasonable fix. Sounds not good at all.

I reject it because your approach is flawed, and that you are
papering over a glaring bug in your driver that you are refusing
to fix.

Maybe the right thing to do is to remove this driver from the code
base altogether. I will prepare a patch to that effect.

         M.

Patch
diff mbox series

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))