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>
This commit is contained in:
parent
5d13f62b9e
commit
f2323c374e
|
@ -1882,6 +1882,42 @@ static struct sched_domain *build_sched_domain(struct sched_domain_topology_leve
|
|||
return sd;
|
||||
}
|
||||
|
||||
/*
|
||||
* Ensure topology masks are sane, i.e. there are no conflicts (overlaps) for
|
||||
* any two given CPUs at this (non-NUMA) topology level.
|
||||
*/
|
||||
static bool topology_span_sane(struct sched_domain_topology_level *tl,
|
||||
const struct cpumask *cpu_map, int cpu)
|
||||
{
|
||||
int i;
|
||||
|
||||
/* NUMA levels are allowed to overlap */
|
||||
if (tl->flags & SDTL_OVERLAP)
|
||||
return true;
|
||||
|
||||
/*
|
||||
* Non-NUMA levels cannot partially overlap - they must be either
|
||||
* completely equal or completely disjoint. Otherwise we can end up
|
||||
* breaking the sched_group lists - i.e. a later get_group() pass
|
||||
* breaks the linking done for an earlier span.
|
||||
*/
|
||||
for_each_cpu(i, cpu_map) {
|
||||
if (i == cpu)
|
||||
continue;
|
||||
/*
|
||||
* We should 'and' all those masks with 'cpu_map' to exactly
|
||||
* match the topology we're about to build, but that can only
|
||||
* remove CPUs, which only lessens our ability to detect
|
||||
* overlaps
|
||||
*/
|
||||
if (!cpumask_equal(tl->mask(cpu), tl->mask(i)) &&
|
||||
cpumask_intersects(tl->mask(cpu), tl->mask(i)))
|
||||
return false;
|
||||
}
|
||||
|
||||
return true;
|
||||
}
|
||||
|
||||
/*
|
||||
* Find the sched_domain_topology_level where all CPU capacities are visible
|
||||
* for all CPUs.
|
||||
|
@ -1978,6 +2014,9 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
|
|||
has_asym = true;
|
||||
}
|
||||
|
||||
if (WARN_ON(!topology_span_sane(tl, cpu_map, i)))
|
||||
goto error;
|
||||
|
||||
sd = build_sched_domain(tl, cpu_map, attr, sd, dflags, i);
|
||||
|
||||
if (tl == sched_domain_topology)
|
||||
|
|
Loading…
Reference in New Issue