[PATCH 5/5] arch_topology: Build cacheinfo from primary CPU

Pierre Gondois
2022-11-08T11:07:07Z

commit 3fcbf1c77d08 ("arch_topology: Fix cache attributes detection
in the CPU hotplug path")
adds a call to detect_cache_attributes() to populate the cacheinfo
before updating the siblings mask. detect_cache_attributes() allocates
memory and can take the PPTT mutex (on ACPI platforms). On PREEMPT_RT
kernels, on secondary CPUs, this triggers a:
'BUG: sleeping function called from invalid context' [1]
as the code is executed with preemption and interrupts disabled.

The primary CPU was previously storing the cache information using
the now removed (struct cpu_topology).llc_id:
commit 5b8dc787ce4a ("arch_topology: Drop LLC identifier stash from
the CPU topology")

allocate_cache_info() tries to build the cacheinfo from the primary
CPU prior secondary CPUs boot, if the DT/ACPI description
contains cache information.
If allocate_cache_info() fails, then fallback to the current state
for the cacheinfo allocation. [1] will be triggered in such case.

When unplugging a CPU, the cacheinfo memory cannot be freed. If it
was, then the memory would be allocated early by the re-plugged
CPU and would trigger [1].

[1]:
[ 7.560791] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
[ 7.560794] in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 0, name: swapper/111
[ 7.560796] preempt_count: 1, expected: 0
[ 7.560797] RCU nest depth: 1, expected: 1
[ 7.560799] 3 locks held by swapper/111/0:
[ 7.560800] #0: ffff403e406cae98 (&pcp->lock){+.+.}-{3:3}, at: get_page_from_freelist+0x218/0x12c8
[ 7.560811] #1: ffffc5f8ed09f8e8 (rcu_read_lock){....}-{1:3}, at: rt_spin_trylock+0x48/0xf0
[ 7.560820] #2: ffff403f400b4fd8 (&zone->lock){+.+.}-{3:3}, at: rmqueue_bulk+0x64/0xa80
[ 7.560824] irq event stamp: 0
[ 7.560825] hardirqs last enabled at (0): [<0000000000000000>] 0x0
[ 7.560827] hardirqs last disabled at (0): [<ffffc5f8e9f7d594>] copy_process+0x5dc/0x1ab8
[ 7.560830] softirqs last enabled at (0): [<ffffc5f8e9f7d594>] copy_process+0x5dc/0x1ab8
[ 7.560833] softirqs last disabled at (0): [<0000000000000000>] 0x0
[ 7.560834] Preemption disabled at:
[ 7.560835] [<ffffc5f8e9fd3c28>] migrate_enable+0x30/0x130
[ 7.560838] CPU: 111 PID: 0 Comm: swapper/111 Tainted: G W 6.0.0-rc4-rt6-[...]
[ 7.560841] Call trace:
[...]
[ 7.560870] __kmalloc+0xbc/0x1e8
[ 7.560873] detect_cache_attributes+0x2d4/0x5f0
[ 7.560876] update_siblings_masks+0x30/0x368
[ 7.560880] store_cpu_topology+0x78/0xb8
[ 7.560883] secondary_start_kernel+0xd0/0x198
[ 7.560885] __secondary_switched+0xb0/0xb4

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
---
drivers/base/arch_topology.c | 10 ++++++-
drivers/base/cacheinfo.c | 53 ++++++++++++++++++++++++++++--------
include/linux/cacheinfo.h | 1 +
3 files changed, 52 insertions(+), 12 deletions(-)

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index d07a7cfa389a..4222a6d1e07b 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -825,7 +825,7 @@ __weak int __init parse_acpi_topology(void)
#if defined(CONFIG_ARM64) || defined(CONFIG_RISCV)
void __init init_cpu_topology(void)
{
- int ret;
+ int cpu, ret;

reset_cpu_topology();
ret = parse_acpi_topology();
@@ -840,6 +840,14 @@ void __init init_cpu_topology(void)
reset_cpu_topology();
return;
}
+
+ for_each_possible_cpu(cpu) {
+ ret = allocate_cache_info(cpu);
+ if (ret) {
+ pr_err("Early cacheinfo failed, ret = %d\n", ret);
+ break;
+ }
+ }
}

void store_cpu_topology(unsigned int cpuid)
diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index 6f6cd120c4f1..889d94d89e18 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -371,10 +371,6 @@ static void free_cache_attributes(unsigned int cpu)
return;

cache_shared_cpu_map_remove(cpu);
-
- kfree(per_cpu_cacheinfo(cpu));
- per_cpu_cacheinfo(cpu) = NULL;
- cache_leaves(cpu) = 0;
}

int __weak init_cache_level(unsigned int cpu)
@@ -387,18 +383,53 @@ int __weak populate_cache_leaves(unsigned int cpu)
return -ENOENT;
}

+int allocate_cache_info(unsigned int cpu)
+{
+ struct cpu_cacheinfo *this_cpu_ci;
+ unsigned int levels, split_levels;
+ int ret;
+
+ if (acpi_disabled)
+ ret = init_of_cache_level(cpu);
+ else {
+ ret = acpi_get_cache_info(cpu, &levels, &split_levels);
+ this_cpu_ci = get_cpu_cacheinfo(cpu);
+ this_cpu_ci->num_levels = levels;
+ /*
+ * This assumes that:
+ * - there cannot be any split caches (data/instruction)
+ * above a unified cache
+ * - data/instruction caches come by pair
+ */
+ this_cpu_ci->num_leaves = levels + split_levels;
+ }
+ if (ret < 0)
+ return ret;
+ else if (!cache_leaves(cpu))
+ return -ENOENT;
+
+ per_cpu_cacheinfo(cpu) = kcalloc(cache_leaves(cpu),
+ sizeof(struct cacheinfo), GFP_ATOMIC);
+ if (per_cpu_cacheinfo(cpu) == NULL) {
+ cache_leaves(cpu) = 0;
+ return -ENOMEM;
+ }
+
+ return ret;
+}
+
int detect_cache_attributes(unsigned int cpu)
{
int ret;

- /* Since early detection of the cacheinfo is allowed via this
- * function and this also gets called as CPU hotplug callbacks via
- * cacheinfo_cpu_online, the initialisation can be skipped and only
- * CPU maps can be updated as the CPU online status would be update
- * if called via cacheinfo_cpu_online path.
+ /* Since early initialization/allocation of the cacheinfo is allowed
+ * via allocate_cache_info() and this also gets called as CPU hotplug
+ * callbacks via cacheinfo_cpu_online, the init/alloc can be skipped
+ * as it will happen only once (the cacheinfo memory is never freed).
+ * Just populate the cacheinfo.
*/
if (per_cpu_cacheinfo(cpu))
- goto update_cpu_map;
+ goto populate_leaves;

if (init_cache_level(cpu) || !cache_leaves(cpu))
return -ENOENT;
@@ -410,6 +441,7 @@ int detect_cache_attributes(unsigned int cpu)
return -ENOMEM;
}

+populate_leaves:
/*
* populate_cache_leaves() may completely setup the cache leaves and
* shared_cpu_map or it may leave it partially setup.
@@ -418,7 +450,6 @@ int detect_cache_attributes(unsigned int cpu)
if (ret)
goto free_ci;

-update_cpu_map:
/*
* For systems using DT for cache hierarchy, fw_token
* and shared_cpu_map will be set up here only if they are
diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h
index f992d81d211f..7d390806b788 100644
--- a/include/linux/cacheinfo.h
+++ b/include/linux/cacheinfo.h
@@ -85,6 +85,7 @@ int populate_cache_leaves(unsigned int cpu);
int cache_setup_acpi(unsigned int cpu);
bool last_level_cache_is_valid(unsigned int cpu);
bool last_level_cache_is_shared(unsigned int cpu_x, unsigned int cpu_y);
+int allocate_cache_info(unsigned int cpu);
int detect_cache_attributes(unsigned int cpu);
#ifndef CONFIG_ACPI_PPTT
/*
--
2.25.1