• Pierre Gondois's avatar
    arch_topology: Build cacheinfo from primary CPU · 5944ce09
    Pierre Gondois authored
    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.comSigned-off-by: default avatarSudeep Holla <sudeep.holla@arm.com>
    5944ce09
arch_topology.c 21.1 KB