Change Details

schedinit_ap() sets up an AP for a later call to sched_throw(NULL). Currently, ULE sets up some pcpu bits and fixes the idlethread lock with a call to sched_throw(NULL); this creates a window where curthread is setup but it has the wrong td_lock. Typical platform AP startup procedure looks something like: - Setup curthread - ... other stuff, including cpu_initclocks_ap() - Signal smp_started - sched_throw(NULL) to enter the scheduler cpu_initclocks_ap() may have callouts to process (e.g., nvme) and attempt to sched_add() for this AP, but this attempt fails because of the noted violated assumption leading to locking heartburn in sched_setpreempt(). Interrupts are still disabled until cpu_throw() so we're not really at risk of being preempted -- just let the scheduler in on it a little earlier.

schedinit_ap() sets up an AP for a later call to sched_throw(NULL). Currently, ULE sets up some pcpu bits and fixes the idlethread lock with a call to sched_throw(NULL); this creates a window where curthread is setup but it has the wrong td_lock. Typical platform AP startup procedure looks something like: - Setup curthread - ... other stuff, including cpu_initclocks_ap() - Signal smp_started - sched_throw(NULL) to enter the scheduler cpu_initclocks_ap() may have callouts to process (e.g., nvme) and attempt to sched_add() for this AP, but this attempt fails because of the noted violated assumption leading to locking heartburn in sched_setpreempt(). Interrupts are still disabled until cpu_throw() so we're not really at risk of being preempted -- just let the scheduler in on it a little earlier.

schedinit_ap() sets up an AP for a later call to sched_throw(NULL). Currently, ULE sets up some pcpu bits and fixes the idlethread lock with a call to sched_throw(NULL); this creates a window where curthread is setup but it has the wrong td_lock. Typical platform AP startup procedure looks something like: - Setup curthread - ... other stuff, including cpu_initclocks_ap() - Signal smp_started - sched_throw(NULL) to enter the scheduler cpu_initclocks_ap() may have callouts to process (e.g., nvme) and attempt to sched_add() for this AP, but this attempt fails because of the noted violated assumption leading to locking heartburn in sched_setpreempt(). Interrupts are still disabled until cpu_throw() so we're not really at risk of being preempted -- just let the scheduler in on it a little earlier.