Messages in this thread | | | Date | Wed, 05 Aug 2020 09:17:38 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH 1/1] arm64: kexec: no need to do irq_chip->irq_mask if it already masked |
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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. -- Jazz is not dead. It just smells funny...
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