Scheduling: OR in SCHED_RESET_ON_FORK instead of ANDing it

[winklemad]

Description

Scheduling_setPolicy() sets the reset-on-fork flag with &= instead of |=:

#ifdef SCHED_RESET_ON_FORK
if (reset_on_fork)
   policy &= SCHED_RESET_ON_FORK;   // should be |=
#endif

SCHED_RESET_ON_FORK is 0x40000000, and the scheduling policies (SCHED_OTHER=0, FIFO=1, RR=2, BATCH=3, IDLE=5) share no bits with it, so policy &= 0x40000000 is always 0 (SCHED_OTHER) — the chosen policy and the flag are both lost.

So when a user enables "Reset on fork" and selects a real-time policy (FIFO/RR/BATCH/IDLE), the subsequent sched_setscheduler(pid, SCHED_OTHER, {sched_priority > 0}) fails with EINVAL (a nonzero priority is invalid for SCHED_OTHER) and the action silently fails; with priority 0 the process is silently downgraded to SCHED_OTHER. Either way, neither the requested policy nor reset-on-fork is applied.

Fix

Use |= so the flag is OR-ed onto the chosen policy — matching the sibling Scheduling_formatPolicy(), which strips it back out with policy & ~SCHED_RESET_ON_FORK, confirming it's meant to be combined.

Verification

The block is Linux-only (#ifdef SCHED_RESET_ON_FORK inside SCHEDULER_SUPPORT), so I confirmed the bitwise logic with a small harness rather than the live UI: for every policy, the current &= yields 0x00000000 (policy lost) while |= yields the correct 0x40000000 | policy (e.g. FIFO → 0x40000001). htop builds cleanly before/after. A repo-wide grep confirms this is the only &= used to set (rather than clear) a flag.

This fix was prepared with AI assistance (noted via the Assisted-by: commit trailer, per the project's policy); I reviewed the change and verified the logic and the reproduction myself.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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Reviewing files that changed from the base of the PR and between a97ad96 and 4dc18e7.

📒 Files selected for processing (1)

• Scheduling.c

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📝 Walkthrough

Walkthrough

Scheduling_setPolicy now uses bitwise OR to apply SCHED_RESET_ON_FORK, preserving all existing scheduling policy bits when reset_on_fork is enabled.

Poem

A policy flag joins the stream,
Existing bits remain supreme.
Reset-on-fork now takes its place,
Without erasing the policy’s face.

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