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Thomas Gleixner e43b3b5854 genirq/cpuhotplug: Enforce affinity setting on startup of managed irqs
Managed interrupts can end up in a stale state on CPU hotplug. If the
interrupt is not targeting a single CPU, i.e. the affinity mask spawns
multiple CPUs then the following can happen:

After boot:

dstate:   0x01601200
            IRQD_ACTIVATED
            IRQD_IRQ_STARTED
            IRQD_SINGLE_TARGET
            IRQD_AFFINITY_SET
            IRQD_AFFINITY_MANAGED
node:     0
affinity: 24-31
effectiv: 24
pending:  0

After offlining CPU 31 - 24

dstate:   0x01a31000
            IRQD_IRQ_DISABLED
            IRQD_IRQ_MASKED
            IRQD_SINGLE_TARGET
            IRQD_AFFINITY_SET
            IRQD_AFFINITY_MANAGED
            IRQD_MANAGED_SHUTDOWN
node:     0
affinity: 24-31
effectiv: 24
pending:  0

Now CPU 25 gets onlined again, so it should get the effective interrupt
affinity for this interruopt, but due to the x86 interrupt affinity setter
restrictions this ends up after restarting the interrupt with:

dstate:   0x01601300
            IRQD_ACTIVATED
            IRQD_IRQ_STARTED
            IRQD_SINGLE_TARGET
            IRQD_AFFINITY_SET
            IRQD_SETAFFINITY_PENDING
            IRQD_AFFINITY_MANAGED
node:     0
affinity: 24-31
effectiv: 24
pending:  24-31

So the interrupt is still affine to CPU 24, which was the last CPU to go
offline of that affinity set and the move to an online CPU within 24-31,
in this case 25, is pending. This mechanism is x86/ia64 specific as those
architectures cannot move interrupts from thread context and do this when
an interrupt is actually handled. So the move is set to pending.

Whats worse is that offlining CPU 25 again results in:

dstate:   0x01601300
            IRQD_ACTIVATED
            IRQD_IRQ_STARTED
            IRQD_SINGLE_TARGET
            IRQD_AFFINITY_SET
            IRQD_SETAFFINITY_PENDING
            IRQD_AFFINITY_MANAGED
node:     0
affinity: 24-31
effectiv: 24
pending:  24-31

This means the interrupt has not been shut down, because the outgoing CPU
is not in the effective affinity mask, but of course nothing notices that
the effective affinity mask is pointing at an offline CPU.

In the case of restarting a managed interrupt the move restriction does not
apply, so the affinity setting can be made unconditional. This needs to be
done _before_ the interrupt is started up as otherwise the condition for
moving it from thread context would not longer be fulfilled.

With that change applied onlining CPU 25 after offlining 31-24 results in:

dstate:   0x01600200
            IRQD_ACTIVATED
            IRQD_IRQ_STARTED
            IRQD_SINGLE_TARGET
            IRQD_AFFINITY_MANAGED
node:     0
affinity: 24-31
effectiv: 25
pending:  

And after offlining CPU 25:

dstate:   0x01a30000
            IRQD_IRQ_DISABLED
            IRQD_IRQ_MASKED
            IRQD_SINGLE_TARGET
            IRQD_AFFINITY_MANAGED
            IRQD_MANAGED_SHUTDOWN
node:     0
affinity: 24-31
effectiv: 25
pending:  

which is the correct and expected result.

Fixes: 761ea388e8 ("genirq: Handle managed irqs gracefully in irq_startup()")
Reported-by: YASUAKI ISHIMATSU <yasu.isimatu@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: axboe@kernel.dk
Cc: linux-scsi@vger.kernel.org
Cc: Sumit Saxena <sumit.saxena@broadcom.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: mpe@ellerman.id.au
Cc: Shivasharan Srikanteshwara <shivasharan.srikanteshwara@broadcom.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: keith.busch@intel.com
Cc: peterz@infradead.org
Cc: Hannes Reinecke <hare@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1710042208400.2406@nanos
2017-10-09 13:26:48 +02:00
arch ARC udpates for 4.14-rc4 2017-10-06 15:57:08 -07:00
block bsg-lib: fix use-after-free under memory-pressure 2017-10-04 08:35:04 -06:00
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ipc fix a typo in put_compat_shm_info() 2017-09-25 20:41:46 -04:00
kernel genirq/cpuhotplug: Enforce affinity setting on startup of managed irqs 2017-10-09 13:26:48 +02:00
lib lib/ratelimit.c: use deferred printk() version 2017-10-03 17:54:26 -07:00
mm mm/memory_hotplug: define find_{smallest|biggest}_section_pfn as unsigned long 2017-10-03 17:54:26 -07:00
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virt Revert "KVM: Don't accept obviously wrong gsi values via KVM_IRQFD" 2017-09-19 08:37:17 +02:00
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Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.