diff options
| author | Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | 2020-10-20 09:47:14 -0400 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2020-10-29 11:00:31 +0100 |
| commit | 618758ed3a4f7d790414d020b362111748ebbf9f (patch) | |
| tree | 9357b04f04a5ef25a162bed531eedce691339280 /kernel/kthread.c | |
| parent | 5bc78502322a5e4eef3f1b2a2813751dc6434143 (diff) | |
sched: membarrier: cover kthread_use_mm (v4)
Add comments and memory barrier to kthread_use_mm and kthread_unuse_mm
to allow the effect of membarrier(2) to apply to kthreads accessing
user-space memory as well.
Given that no prior kthread use this guarantee and that it only affects
kthreads, adding this guarantee does not affect user-space ABI.
Refine the check in membarrier_global_expedited to exclude runqueues
running the idle thread rather than all kthreads from the IPI cpumask.
Now that membarrier_global_expedited can IPI kthreads, the scheduler
also needs to update the runqueue's membarrier_state when entering lazy
TLB state.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201020134715.13909-3-mathieu.desnoyers@efficios.com
Diffstat (limited to 'kernel/kthread.c')
| -rw-r--r-- | kernel/kthread.c | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/kernel/kthread.c b/kernel/kthread.c index e29773c82b70..481428fe5f22 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -1248,6 +1248,7 @@ void kthread_use_mm(struct mm_struct *mm) tsk->active_mm = mm; } tsk->mm = mm; + membarrier_update_current_mm(mm); switch_mm_irqs_off(active_mm, mm, tsk); local_irq_enable(); task_unlock(tsk); @@ -1255,8 +1256,19 @@ void kthread_use_mm(struct mm_struct *mm) finish_arch_post_lock_switch(); #endif + /* + * When a kthread starts operating on an address space, the loop + * in membarrier_{private,global}_expedited() may not observe + * that tsk->mm, and not issue an IPI. Membarrier requires a + * memory barrier after storing to tsk->mm, before accessing + * user-space memory. A full memory barrier for membarrier + * {PRIVATE,GLOBAL}_EXPEDITED is implicitly provided by + * mmdrop(), or explicitly with smp_mb(). + */ if (active_mm != mm) mmdrop(active_mm); + else + smp_mb(); to_kthread(tsk)->oldfs = force_uaccess_begin(); } @@ -1276,9 +1288,18 @@ void kthread_unuse_mm(struct mm_struct *mm) force_uaccess_end(to_kthread(tsk)->oldfs); task_lock(tsk); + /* + * When a kthread stops operating on an address space, the loop + * in membarrier_{private,global}_expedited() may not observe + * that tsk->mm, and not issue an IPI. Membarrier requires a + * memory barrier after accessing user-space memory, before + * clearing tsk->mm. + */ + smp_mb__after_spinlock(); sync_mm_rss(mm); local_irq_disable(); tsk->mm = NULL; + membarrier_update_current_mm(NULL); /* active_mm is still 'mm' */ enter_lazy_tlb(mm, tsk); local_irq_enable(); |