sched/affinity: Fix CPU_LOCKED functionality for some SMP calls#16262
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For some SMP calls it is necessary to lock the current CPU for the process
receiving the SMP call. This is done by setting the CPU affinity to the
current CPU and preventing the CPU selection algorithm from switching
CPUs.
dtcb->flags |= TCB_FLAG_CPU_LOCKED;
CPU_SET(dtcb->cpu, &dtcb->affinity);
However, this logic is currently broken, as CPU_SET is defined as:
#define CPU_SET(c,s) do { *(s) |= (1u << (c)); } while (0)
In order to assign tcb->cpu (the current CPU) to the affinity mask, the
mask must be cleared first by calling CPU_ZERO.
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xiaoxiang781216
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Apr 25, 2025
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Summary
For some SMP calls it is necessary to lock the current CPU for the process receiving the SMP call. This is done by setting the CPU affinity to the current CPU and preventing the CPU selection algorithm from switching CPUs.
dtcb->flags |= TCB_FLAG_CPU_LOCKED;
CPU_SET(dtcb->cpu, &dtcb->affinity);
However, this logic is currently broken, as CPU_SET is defined as:
#define CPU_SET(c,s) do { *(s) |= (1u << (c)); } while (0)
In order to assign tcb->cpu (the current CPU) to the affinity mask, the mask must be cleared first by calling CPU_ZERO.
Impact
This fixes a bug in SMP mode where the kernel attempts to lock CPU for a process, but the CPU can still change. Impact
is a bug fix in the kernel. No user / documentation / API changes and so forth.
Testing
Testing and bug hunting was done by @jlaitine by running ostest with SMP enabled. The crash occurs in signest test.
Issues related:
#16193
#16133