[PATCH v5 0/2] irqchip/riscv-aplic: fix probing of multiple APLIC instances

[Vladimir Kondratiev <vladimir.kondratiev@mobileye.com>]

The APLIC driver does not set probe_type, so it follows
PROBE_DEFAULT_STRATEGY and gets probed asynchronously when the command
line asks for it (driver_async_probe=). The probe path of an APLIC
instance modifies state shared by all instances without any locking,
for example the registration of the syscore operations. On a system with
several APLIC instances this triggers a "list_add double add" report from
CHECK_DATA_CORRUPTION, because two instances both call register_syscore()
for the same node.

Looking at the problem showed a second, unrelated issue: the flag guarding
the syscore registration is marked __ro_after_init, but with MSI the probe
can be deferred until the IMSIC is available, and then writes the flag
after init memory was made read-only.

Patch 1 fixes the latter and is independent of asynchronous probing.

Patch 2 marks the driver PROBE_FORCE_SYNCHRONOUS. The shared state also
includes the global aplics list, aplic_direct_parent_irq (together with
the CPU hotplug state registered for it) and the per-CPU IDC structures,
so making probes mutually exclusive is simpler and less error-prone than
adding a lock for each of them. An interrupt controller is needed early
and gains nothing from probing in parallel.

Reproduced by booting with "driver_async_probe=riscv-aplic" on the
not yet upstreamed "Mobileye eyeq7h" platform with 3 APLIC instances.

Signed-off-by: Vladimir Kondratiev <vladimir.kondratiev@mobileye.com>
---
Changes in v5:
- split the __ro_after_init fix out into its own patch
- drop atomic_t/atomic_cmpxchg() for the registration flag
- mark the driver PROBE_FORCE_SYNCHRONOUS instead of protecting each piece
  of shared state separately
- Link to v4: https://patch.msgid.link/20261020-aplic-async-probe-v4-1-68bc35e0ece1@mobileye.com

Changes in v4:
- rework commit message
- rebase onto v7.3
- Link to v3: https://lore.kernel.org/r/20261012-aplic-async-probe-v3-1-5cf52dc28690@mobileye.com

Changes in v3:
- drop __ro_after_init attribute due to write to read-only page concern
- Link to v2: https://lore.kernel.org/r/20261012-aplic-async-probe-v2-1-868d7684c9d6@mobileye.com

Changes in v2:
- fixed potential access to read-only page
- Link to v1: https://lore.kernel.org/r/20261012-aplic-async-probe-v1-1-4c2c4f5b0916@mobileye.com

To: Anup Patel <anup@brainfault.org>
To: Thomas Gleixner <tglx@kernel.org>
To: Radu Rendec <radu@rendec.net>
To: Paul Walmsley <pjw@kernel.org>
To: Palmer Dabbelt <palmer@dabbelt.com>
To: Albert Ou <aou@eecs.berkeley.edu>
To: Alexandre Ghiti <alex@ghiti.fr>
To: Jessica Liu <liu.xuemei1@zte.com.cn>
Cc: linux-riscv@lists.infradead.org
Cc: linux-kernel@vger.kernel.org

---
Vladimir Kondratiev (2):
      irqchip/riscv-aplic: do not mark the syscore registered flag ro_after_init
      irqchip/riscv-aplic: force synchronous probing

 drivers/irqchip/irq-riscv-aplic-main.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)
---
base-commit: c03c1a14507dfaf8b856c2608f9ac216021fc222
change-id: 20261012-aplic-async-probe-81624e035607

Best regards,
--  
Vladimir Kondratiev <vladimir.kondratiev@mobileye.com>