[PATCH] x86/smp: Fix __max_logical_packages value setup

Jiri Olsa
2016-08-10T18:42:35Z

On Wed, Aug 10, 2016 at 05:52:05PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 10, 2016 at 04:15:38PM +0200, Jiri Olsa wrote:
> > it's very likely I'm missing something, but seems to me
> > that attached patch (untested) might work as well
>
> Hmm, I think you're right. Earlier code (which hasn't survived) tried to
> match logical and physical if possible, but that was busted and got
> removed.
>
> The code as is should indeed allow for this.
>
> Maybe one nit, the variable is no longer used for a max, so maybe rename
> it too?

ok, renaming it to logical_packages then, attaching full patch

thanks,
jirka

---
Frank reported kernel panic when he disabled several cores in BIOS
via following option:

Core Disable Bitmap(Hex) [0]

with number 0xFFE, which leaves 16 CPUs in system (out of 48).

The kernel panic below goes along with following messages:

smpboot: Max logical packages: 2^M
smpboot: APIC(0) Converting physical 0 to logical package 0^M
smpboot: APIC(20) Converting physical 1 to logical package 1^M
smpboot: APIC(40) Package 2 exceeds logical package map^M
smpboot: CPU 8 APICId 40 disabled^M
smpboot: APIC(60) Package 3 exceeds logical package map^M
smpboot: CPU 12 APICId 60 disabled^M
...
general protection fault: 0000 [#1] SMP^M
Modules linked in:^M
CPU: 15 PID: 1 Comm: swapper/0 Not tainted 4.7.0-rc5+ #1^M
Hardware name: SGI UV300/UV300, BIOS SGI UV 300 series BIOS 05/25/2016^M
task: ffff8801673e0000 ti: ffff8801673ac000 task.ti: ffff8801673ac000^M
RIP: 0010:[<ffffffff81014d54>] [<ffffffff81014d54>] uncore_change_context+0xd4/0x180^M
...
[<ffffffff810158ac>] uncore_event_init_cpu+0x6c/0x70^M
[<ffffffff81d8c91c>] intel_uncore_init+0x1c2/0x2dd^M
[<ffffffff81d8c75a>] ? uncore_cpu_setup+0x17/0x17^M
[<ffffffff81002190>] do_one_initcall+0x50/0x190^M
[<ffffffff810ab193>] ? parse_args+0x293/0x480^M
[<ffffffff81d87365>] kernel_init_freeable+0x1a5/0x249^M
[<ffffffff81d86a35>] ? set_debug_rodata+0x12/0x12^M
[<ffffffff816dc19e>] kernel_init+0xe/0x110^M
[<ffffffff816e93bf>] ret_from_fork+0x1f/0x40^M
[<ffffffff816dc190>] ? rest_init+0x80/0x80^M

The reason for the panic is wrong value of __max_logical_packages,
which lets logical_package_map uninitialized and the uncore code
relying on this map being properly initialized (maybe we should
add some safety checks there as well).

The __max_logical_packages is computed as:

DIV_ROUND_UP(total_cpus, ncpus);
- ncpus being number of cores

With above BIOS setup we get total_cpus == 16 which set
__max_logical_packages to 2 (ncpus is 12).

Once topology_update_package_map processes CPU with logical
pkg over 2 we display above messages and fail to initialize
the physical_to_logical_pkg map, which makes the uncore code
crash.

The fix is to remove logical_package_map bitmap completely
and just keep and update the logical_packages number.

Reported-by: Frank Ramsay <framsay@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
arch/x86/include/asm/topology.h | 4 ++--
arch/x86/kernel/smpboot.c | 21 +++++----------------
2 files changed, 7 insertions(+), 18 deletions(-)

diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
index cf75871d2f81..c28010088651 100644
--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -118,8 +118,8 @@ extern const struct cpumask *cpu_coregroup_mask(int cpu);
#define topology_core_cpumask(cpu) (per_cpu(cpu_core_map, cpu))
#define topology_sibling_cpumask(cpu) (per_cpu(cpu_sibling_map, cpu))

-extern unsigned int __max_logical_packages;
-#define topology_max_packages() (__max_logical_packages)
+extern unsigned int logical_packages;
+#define topology_max_packages() (logical_packages)

extern int __max_smt_threads;

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 157bf0957219..b1b775dbede6 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -100,10 +100,9 @@ EXPORT_PER_CPU_SYMBOL(cpu_info);
/* Logical package management. We might want to allocate that dynamically */
static int *physical_to_logical_pkg __read_mostly;
static unsigned long *physical_package_map __read_mostly;;
-static unsigned long *logical_package_map __read_mostly;
static unsigned int max_physical_pkg_id __read_mostly;
-unsigned int __max_logical_packages __read_mostly;
-EXPORT_SYMBOL(__max_logical_packages);
+unsigned int logical_packages __read_mostly;
+EXPORT_SYMBOL(logical_packages);

/* Maximum number of SMT threads on any online core */
int __max_smt_threads __read_mostly;
@@ -277,14 +276,8 @@ int topology_update_package_map(unsigned int apicid, unsigned int cpu)
if (test_and_set_bit(pkg, physical_package_map))
goto found;

- new = find_first_zero_bit(logical_package_map, __max_logical_packages);
- if (new >= __max_logical_packages) {
- physical_to_logical_pkg[pkg] = -1;
- pr_warn("APIC(%x) Package %u exceeds logical package map\n",
- apicid, pkg);
- return -ENOSPC;
- }
- set_bit(new, logical_package_map);
+ new = logical_packages++;
+
pr_info("APIC(%x) Converting physical %u to logical package %u\n",
apicid, pkg, new);
physical_to_logical_pkg[pkg] = new;
@@ -340,7 +333,7 @@ static void __init smp_init_package_map(void)
ncpus = 1;
}

- __max_logical_packages = DIV_ROUND_UP(total_cpus, ncpus);
+ logical_packages = 0;

/*
* Possibly larger than what we need as the number of apic ids per
@@ -352,10 +345,6 @@ static void __init smp_init_package_map(void)
memset(physical_to_logical_pkg, 0xff, size);
size = BITS_TO_LONGS(max_physical_pkg_id) * sizeof(unsigned long);
physical_package_map = kzalloc(size, GFP_KERNEL);
- size = BITS_TO_LONGS(__max_logical_packages) * sizeof(unsigned long);
- logical_package_map = kzalloc(size, GFP_KERNEL);
-
- pr_info("Max logical packages: %u\n", __max_logical_packages);

for_each_present_cpu(cpu) {
unsigned int apicid = apic->cpu_present_to_apicid(cpu);
--
2.4.11