[PATCH 0/2] *** cpu/hotplug, riscv: Fix CPU stuck offline after failed hotplug attempt ***

[artemiispatov at gmail.com]

From: Artemii Patov <artemiispatov at gmail.com>

These two patches enable RISC-V to retry bringing an AP
online when the control CPU failed to complete the
SYNC_STATE_ALIVE -> SYNC_STATE_SHOULD_ONLINE transition and
the secondary CPU is stuck spinning in cpuhp_ap_sync_alive().

The need for this arose during debugging RISC-V SoC. Control CPU tried
to wake up a halted CPU and sent an IPI via OpenSBI. The IPI was masked
while the secondary CPU was in Debug Mode; when the CPU left Debug Mode
it saw the pending IPI bit and started processing it. Meanwhile control
CPU did not observe the ALIVE state within the timeout in
cpuhp_bp_sync_alive() and aborted the bringup. The secondary CPU
eventually entered Linux and got stuck spinning in cpuhp_ap_sync_alive().

A retry of the bringup fails due to both the current sync-state
switching in kernel/cpu.c and the incomplete SBI error handling in
arch/riscv/kernel/cpu_ops_sbi.c (see the patches for details). Both
behaviors are addressed by this patchset.

Artemii Patov (2):
  cpu/hotplug: Skip kick stage if the AP is stuck in SYNC_STATE_ALIVE
  riscv: sbi: Accept SBI_ERR_ALREADY_AVAILABLE in sbi_hsm_hart_start

 arch/riscv/include/asm/sbi.h    |  2 ++
 arch/riscv/kernel/cpu_ops_sbi.c |  7 ++++++-
 kernel/cpu.c                    | 17 +++++++++++++++--
 3 files changed, 23 insertions(+), 3 deletions(-)

-- 
2.43.0