Memory barriers before updating rq->curr¶

The commands MEMBARRIER_CMD_PRIVATE_EXPEDITED and MEMBARRIER_CMD_GLOBAL_EXPEDITEDrequire each architecture to have a full memory barrier after coming fromuser-space, before updating rq->curr. This barrier is implied by the sequencerq_lock();smp_mb__after_spinlock() in__schedule(). The barrier matches a fullbarrier in the proximity of the membarrier system call exit, cf.membarrier_{private,global}_expedited().

Memory barriers after updating rq->curr¶

The commands MEMBARRIER_CMD_PRIVATE_EXPEDITED and MEMBARRIER_CMD_GLOBAL_EXPEDITEDrequire each architecture to have a full memory barrier after updating rq->curr,before returning to user-space. The schemes providing this barrier on the variousarchitectures are as follows.

• alpha, arc, arm, hexagon, mips rely on the full barrier implied byspin_unlock() infinish_lock_switch().

• arm64 relies on the full barrier implied byswitch_to().

• powerpc, riscv, s390, sparc, x86 rely on the full barrier implied byswitch_mm(), if mm is not NULL; they rely on the full barrier impliedbymmdrop(), otherwise. On powerpc and riscv,switch_mm() relies onmembarrier_arch_switch_mm().

The barrier matches a full barrier in the proximity of the membarrier system callentry, cf. membarrier_{private,global}_expedited().