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Date: Wed, 7 Jul 2021 11:29:29 +0530
From: Sumit Garg <sumit.garg@...aro.org>
To: wens@...nel.org
Cc: Marc Zyngier <maz@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Daniel Thompson <daniel.thompson@...aro.org>,
Mark Rutland <mark.rutland@....com>, tsbogend@...ha.franken.de,
linux-kernel <linux-kernel@...r.kernel.org>,
Jason Cooper <jason@...edaemon.net>, ito-yuichi@...itsu.com,
mpe@...erman.id.au, x86@...nel.org,
Russell King <linux@...linux.org.uk>,
Douglas Anderson <dianders@...omium.org>,
Ingo Molnar <mingo@...hat.com>, bp@...en8.de,
julien.thierry.kdev@...il.com,
Jason Wessel <jason.wessel@...driver.com>,
kgdb-bugreport@...ts.sourceforge.net,
Thomas Gleixner <tglx@...utronix.de>,
Masayoshi Mizuma <msys.mizuma@...il.com>,
David Miller <davem@...emloft.net>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v7 0/7] arm64: Add framework to turn an IPI as NMI
On Fri, 25 Jun 2021 at 20:26, Chen-Yu Tsai <wens@...nel.org> wrote:
>
> On Mon, Nov 2, 2020 at 7:46 PM Sumit Garg <sumit.garg@...aro.org> wrote:
> >
> > With pseudo NMIs support available its possible to configure SGIs to be
> > triggered as pseudo NMIs running in NMI context. And kernel features
> > such as:
> > - NMI backtrace can leverage IPI turned as NMI to get a backtrace of CPU
> > stuck in hard lockup using magic SYSRQ.
> > - kgdb relies on NMI support to round up CPUs which are stuck in hard
> > lockup state with interrupts disabled.
> >
> > This patch-set adds framework to turn an IPI as NMI which can be triggered
> > as a pseudo NMI which in turn invokes registered NMI handlers.
> >
> > After this patch-set we should be able to get a backtrace for a CPU
> > stuck in HARDLOCKUP. Have a look at an examples below from a hard lockup
> > testcase run on Developerbox:
> >
> > $ echo HARDLOCKUP > /sys/kernel/debug/provoke-crash/DIRECT
> >
> > NMI backtrace:
> > ==============
> >
> > # Issue Magic SysRq to dump backtrace
> >
> > [ 376.894502] NMI backtrace for cpu 8
> > [ 376.894506] CPU: 8 PID: 555 Comm: bash Not tainted 5.9.0-rc3-00740-g06ff047-dirty #242
> > [ 376.894510] Hardware name: Socionext SynQuacer E-series DeveloperBox, BIOS build #73 Apr 6 2020
> > [ 376.894514] pstate: 40000005 (nZcv daif -PAN -UAO BTYPE=--)
> > [ 376.894517] pc : lkdtm_HARDLOCKUP+0x8/0x18
> > [ 376.894520] lr : lkdtm_do_action+0x24/0x30
> > [ 376.894524] sp : ffff800012cebd20
> > [ 376.894527] pmr_save: 00000060
> > [ 376.894530] x29: ffff800012cebd20 x28: ffff000875ae8000
> > [ 376.894540] x27: 0000000000000000 x26: 0000000000000000
> > [ 376.894550] x25: 000000000000001a x24: ffff800012cebe40
> > [ 376.894560] x23: 000000000000000b x22: ffff800010fc5040
> > [ 376.894569] x21: ffff000878b61000 x20: ffff8000113b2870
> > [ 376.894579] x19: 000000000000001b x18: 0000000000000010
> > [ 376.894588] x17: 0000000000000000 x16: 0000000000000000
> > [ 376.894598] x15: ffff000875ae8470 x14: 00000000000002ad
> > [ 376.894613] x13: 0000000000000000 x12: 0000000000000000
> > [ 376.894622] x11: 0000000000000007 x10: 00000000000009c0
> > [ 376.894631] x9 : ffff800012ceba80 x8 : ffff000875ae8a20
> > [ 376.894641] x7 : ffff00087f6b3280 x6 : ffff00087f6b3200
> > [ 376.894651] x5 : 0000000000000000 x4 : ffff00087f6a91f8
> > [ 376.894660] x3 : ffff00087f6b0120 x2 : 1aa310cec69eb500
> > [ 376.894670] x1 : 0000000000000000 x0 : 0000000000000060
> > [ 376.894679] Call trace:
> > [ 376.894683] lkdtm_HARDLOCKUP+0x8/0x18
> > [ 376.894686] direct_entry+0x124/0x1c0
> > [ 376.894689] full_proxy_write+0x60/0xb0
> > [ 376.894693] vfs_write+0xf0/0x230
> > [ 376.894696] ksys_write+0x6c/0xf8
> > [ 376.894699] __arm64_sys_write+0x1c/0x28
> > [ 376.894703] el0_svc_common.constprop.0+0x74/0x1f0
> > [ 376.894707] do_el0_svc+0x24/0x90
> > [ 376.894710] el0_sync_handler+0x180/0x2f8
> > [ 376.894713] el0_sync+0x158/0x180
> >
> > KGDB:
> > =====
> >
> > # Enter kdb via Magic SysRq
> >
> > [6]kdb> btc
> > btc: cpu status: Currently on cpu 6
> > Available cpus: 0-5(I), 6, 7(I), 8, 9-23(I)
> > <snip>
> > Stack traceback for pid 555
> > 0xffff000875ae8000 555 554 1 8 R 0xffff000875ae89c0 bash
> > CPU: 8 PID: 555 Comm: bash Not tainted 5.9.0-rc3-00740-g06ff047-dirty #242
> > Hardware name: Socionext SynQuacer E-series DeveloperBox, BIOS build #73 Apr 6 2020
> > Call trace:
> > dump_backtrace+0x0/0x1a0
> > show_stack+0x18/0x28
> > dump_stack+0xc0/0x11c
> > kgdb_cpu_enter+0x648/0x660
> > kgdb_nmicallback+0xa0/0xa8
> > ipi_kgdb_nmicallback+0x24/0x30
> > ipi_nmi_handler+0x48/0x60
> > handle_percpu_devid_fasteoi_ipi+0x74/0x88
> > generic_handle_irq+0x30/0x48
> > handle_domain_nmi+0x48/0x80
> > gic_handle_irq+0x18c/0x34c
> > el1_irq+0xcc/0x180
> > lkdtm_HARDLOCKUP+0x8/0x18
> > direct_entry+0x124/0x1c0
> > full_proxy_write+0x60/0xb0
> > vfs_write+0xf0/0x230
> > ksys_write+0x6c/0xf8
> > __arm64_sys_write+0x1c/0x28
> > el0_svc_common.constprop.0+0x74/0x1f0
> > do_el0_svc+0x24/0x90
> > el0_sync_handler+0x180/0x2f8
> > el0_sync+0x158/0x180
> > <snip>
> >
> > Changes in v7:
> > - Add a new library function: kgdb_smp_call_nmi_hook() to expose fallback
> > mechanism to arch specific code.
> > - Addressed other misc comments from Daniel.
> >
> > Changes in v6:
> > - Two new patches: #4 and #6 which adds runtime fallback framework for
> > sysrq backtrace and kgdb roundup features.
> > - Reversed order of NMI backtrace and kgdb roundup feaure patches.
> > - Addressed other misc. comments from Marc.
> > - I haven't picked any tags from v5 since I think there is major rework
> > involved. Masayoshi, could you please confirm if these features still
> > work for you?
> >
> > Changes in v5:
> > - Rebased to head of upstream master.
> > - Remove redundant invocation of ipi_nmi_setup().
> > - Addressed misc. comments.
> >
> > Changes in v4:
> > - Move IPI NMI framework to a separate file.
> > - Get rid of hard-coded IPI_CALL_NMI_FUNC allocation.
> > - Add NMI backtrace support leveraged via magic SYSRQ.
> >
> > Changes in v3:
> > - Rebased to Marc's latest IPIs patch-set [1].
> >
> > [1] https://lkml.org/lkml/2020/9/1/603
> >
> > Changes since RFC version [1]:
> > - Switch to use generic interrupt framework to turn an IPI as NMI.
> > - Dependent on Marc's patch-set [2] which turns IPIs into normal
> > interrupts.
> > - Addressed misc. comments from Doug on patch #4.
> > - Posted kgdb NMI printk() fixup separately which has evolved since
> > to be solved using different approach via changing kgdb interception
> > of printk() in common printk() code (see patch [3]).
> >
> > [1] https://lkml.org/lkml/2020/4/24/328
> > [2] https://lkml.org/lkml/2020/5/19/710
> > [3] https://lkml.org/lkml/2020/5/20/418
> >
> > Sumit Garg (7):
> > arm64: Add framework to turn IPI as NMI
> > irqchip/gic-v3: Enable support for SGIs to act as NMIs
> > arm64: smp: Assign and setup an IPI as NMI
> > nmi: backtrace: Allow runtime arch specific override
> > arm64: ipi_nmi: Add support for NMI backtrace
> > kgdb: Expose default CPUs roundup fallback mechanism
> > arm64: kgdb: Roundup cpus using IPI as NMI
>
> Tested-by: Chen-Yu Tsai <wens@...e.org>
>
> on an ROC-RK3399-PC.
Thanks for testing this feature.
-Sumit
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