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Valentin Schneider 330a4a7e2b sched/topology: Assert non-NUMA topology masks don't (partially) overlap 
[ Upstream commit ccf74128d6 ]

topology.c::get_group() relies on the assumption that non-NUMA domains do
not partially overlap. Zeng Tao pointed out in [1] that such topology
descriptions, while completely bogus, can end up being exposed to the
scheduler.

In his example (8 CPUs, 2-node system), we end up with:
  MC span for CPU3 == 3-7
  MC span for CPU4 == 4-7

The first pass through get_group(3, sdd@MC) will result in the following
sched_group list:

  3 -> 4 -> 5 -> 6 -> 7
  ^                  /
   `----------------'

And a later pass through get_group(4, sdd@MC) will "corrupt" that to:

  3 -> 4 -> 5 -> 6 -> 7
       ^             /
	`-----------'

which will completely break things like 'while (sg != sd->groups)' when
using CPU3's base sched_domain.

There already are some architecture-specific checks in place such as
x86/kernel/smpboot.c::topology.sane(), but this is something we can detect
in the core scheduler, so it seems worthwhile to do so.

Warn and abort the construction of the sched domains if such a broken
topology description is detected. Note that this is somewhat
expensive (O(t.c²), 't' non-NUMA topology levels and 'c' CPUs) and could be
gated under SCHED_DEBUG if deemed necessary.

Testing
=======

Dietmar managed to reproduce this using the following qemu incantation:

  $ qemu-system-aarch64 -kernel ./Image -hda ./qemu-image-aarch64.img \
  -append 'root=/dev/vda console=ttyAMA0 loglevel=8 sched_debug' -smp \
  cores=8 --nographic -m 512 -cpu cortex-a53 -machine virt -numa \
  node,cpus=0-2,nodeid=0 -numa node,cpus=3-7,nodeid=1

alongside the following drivers/base/arch_topology.c hack (AIUI wouldn't be
needed if '-smp cores=X, sockets=Y' would work with qemu):

8<---
@@ -465,6 +465,9 @@ void update_siblings_masks(unsigned int cpuid)
 		if (cpuid_topo->package_id != cpu_topo->package_id)
 			continue;

+		if ((cpu < 4 && cpuid > 3) || (cpu > 3 && cpuid < 4))
+			continue;
+
 		cpumask_set_cpu(cpuid, &cpu_topo->core_sibling);
 		cpumask_set_cpu(cpu, &cpuid_topo->core_sibling);

8<---

[1]: https://lkml.kernel.org/r/1577088979-8545-1-git-send-email-prime.zeng@hisilicon.com

Reported-by: Zeng Tao <prime.zeng@hisilicon.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200115160915.22575-1-valentin.schneider@arm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2020-02-24 08:38:34 +01:00
arch arm64: dts: ti: k3-j721e-main: Add missing power-domains for smmu 2020-02-24 08:38:34 +01:00
block block, bfq: do not plug I/O for bfq_queues with no proc refs 2020-02-24 08:38:09 +01:00
certs certs: Add wrapper function to check blacklisted binary hash 2019-11-12 12:25:50 +11:00
crypto crypto: essiv - fix AEAD capitalization and preposition use in help text 2020-02-24 08:38:32 +01:00
Documentation fbdev: fix numbering of fbcon options 2020-02-24 08:38:21 +01:00
drivers EDAC/sifive: Fix return value check in ecc_register() 2020-02-24 08:38:33 +01:00
fs f2fs: free sysfs kobject 2020-02-24 08:38:31 +01:00
include raid6/test: fix a compilation warning 2020-02-24 08:38:27 +01:00
init Revert "um: Enable CONFIG_CONSTRUCTORS" 2020-02-01 09:33:00 +00:00
ipc ipc/msg.c: consolidate all xxxctl_down() functions 2020-02-11 04:36:39 -08:00
kernel sched/topology: Assert non-NUMA topology masks don't (partially) overlap 2020-02-24 08:38:34 +01:00
lib raid6/test: fix a compilation warning 2020-02-24 08:38:27 +01:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm/mmu_gather: invalidate TLB correctly on batch allocation failure and flush 2020-02-11 04:37:14 -08:00
net bpf: Return -EBADRQC for invalid map type in __bpf_tx_xdp_map 2020-02-24 08:38:29 +01:00
samples samples/bpf: Set -fno-stack-protector when building BPF programs 2020-02-24 08:38:15 +01:00
scripts kbuild: remove *.tmp file when filechk fails 2020-02-24 08:38:31 +01:00
security selinux: ensure we cleanup the internal AVC counters on error in avc_update() 2020-02-24 08:38:19 +01:00
sound ALSA: usb-audio: add implicit fb quirk for MOTU M Series 2020-02-24 08:38:32 +01:00
tools selftests: Uninitialized variable in test_cgcore_proc_migration() 2020-02-24 08:38:24 +01:00
usr gen_initramfs_list.sh: fix 'bad variable name' error 2020-01-04 00:00:48 +09:00
virt KVM: arm64: Treat emulated TVAL TimerValue as a signed 32-bit integer 2020-02-14 16:53:04 -05:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore modpost: dump missing namespaces into a single modules.nsdeps file 2019-11-11 20:10:01 +09:00
.mailmap MAINTAINERS: update my email address 2020-01-11 14:33:39 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Linux 5.4-rc4 2019-10-29 04:43:29 -06:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: correct entries for ISDN/mISDN section 2020-02-11 04:36:38 -08:00
Makefile Linux 5.5.5 2020-02-19 19:54:14 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

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.