Commit 5944ce09 authored by Pierre Gondois's avatar Pierre Gondois Committed by Sudeep Holla
Browse files

arch_topology: Build cacheinfo from primary CPU 



commit 3fcbf1c7 ("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 5b8dc787 ("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].

Note that populate_cache_leaves() might be called multiple times
due to populate_leaves being moved up. This is required since
detect_cache_attributes() might be called with per_cpu_cacheinfo(cpu)
being allocated but not populated.

[1]:
 | BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
 | in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 0, name: swapper/111
 | preempt_count: 1, expected: 0
 | RCU nest depth: 1, expected: 1
 | 3 locks held by swapper/111/0:
 |  #0:  (&pcp->lock){+.+.}-{3:3}, at: get_page_from_freelist+0x218/0x12c8
 |  #1:  (rcu_read_lock){....}-{1:3}, at: rt_spin_trylock+0x48/0xf0
 |  #2:  (&zone->lock){+.+.}-{3:3}, at: rmqueue_bulk+0x64/0xa80
 | irq event stamp: 0
 | hardirqs last  enabled at (0):  0x0
 | hardirqs last disabled at (0):  copy_process+0x5dc/0x1ab8
 | softirqs last  enabled at (0):  copy_process+0x5dc/0x1ab8
 | softirqs last disabled at (0):  0x0
 | Preemption disabled at:
 |  migrate_enable+0x30/0x130
 | CPU: 111 PID: 0 Comm: swapper/111 Tainted: G        W          6.0.0-rc4-rt6-[...]
 | Call trace:
 |  __kmalloc+0xbc/0x1e8
 |  detect_cache_attributes+0x2d4/0x5f0
 |  update_siblings_masks+0x30/0x368
 |  store_cpu_topology+0x78/0xb8
 |  secondary_start_kernel+0xd0/0x198
 |  __secondary_switched+0xb0/0xb4

Signed-off-by: default avatarPierre Gondois <pierre.gondois@arm.com>
Reviewed-by: default avatarSudeep Holla <sudeep.holla@arm.com>
Acked-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
Link: https://lore.kernel.org/r/20230104183033.755668-7-pierre.gondois@arm.com


Signed-off-by: default avatarSudeep Holla <sudeep.holla@arm.com>
parent bd500361

arch/riscv/kernel/cacheinfo.c

+0 −5
Original line number Diff line number Diff line
@@ -113,11 +113,6 @@ static void fill_cacheinfo(struct cacheinfo **this_leaf, 
	}

}



int init_cache_level(unsigned int cpu)

{

	return init_of_cache_level(cpu);

}



int populate_cache_leaves(unsigned int cpu)

{

	struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);

drivers/base/arch_topology.c

+10 −2
Original line number Diff line number Diff line
@@ -736,7 +736,7 @@ void update_siblings_masks(unsigned int cpuid) 


	ret = detect_cache_attributes(cpuid);

	if (ret && ret != -ENOENT)

		pr_info("Early cacheinfo failed, ret = %d\n", ret);

		pr_info("Early cacheinfo allocation failed, ret = %d\n", ret);



	/* update core and thread sibling masks */

	for_each_online_cpu(cpu) {
@@ -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 = fetch_cache_info(cpu);

		if (ret) {

			pr_err("Early cacheinfo failed, ret = %d\n", ret);

			break;

		}

	}

}



void store_cpu_topology(unsigned int cpuid)

drivers/base/cacheinfo.c

+54 −17
Original line number Diff line number Diff line
@@ -389,10 +389,6 @@ 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)
@@ -405,29 +401,71 @@ int __weak populate_cache_leaves(unsigned int cpu) 
	return -ENOENT;

}



static inline

int allocate_cache_info(int cpu)

{

	per_cpu_cacheinfo(cpu) = kcalloc(cache_leaves(cpu),

					 sizeof(struct cacheinfo), GFP_ATOMIC);

	if (!per_cpu_cacheinfo(cpu)) {

		cache_leaves(cpu) = 0;

		return -ENOMEM;

	}



	return 0;

}



int fetch_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);

		if (ret < 0)

			return ret;

	} else {

		ret = acpi_get_cache_info(cpu, &levels, &split_levels);

		if (ret < 0)

			return ret;



		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 (!cache_leaves(cpu))

		return -ENOENT;



	return allocate_cache_info(cpu);

}



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 fetch_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;



	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;

	}

	ret = allocate_cache_info(cpu);

	if (ret)

		return ret;



populate_leaves:

	/*

	 * populate_cache_leaves() may completely setup the cache leaves and

	 * shared_cpu_map or it may leave it partially setup.
@@ -436,7 +474,6 @@ 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

include/linux/cacheinfo.h

+1 −0
Original line number Diff line number Diff line
@@ -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 fetch_cache_info(unsigned int cpu);

int detect_cache_attributes(unsigned int cpu);

#ifndef CONFIG_ACPI_PPTT

/*