Argh, forgot to cc the userfaultfd people. Sorry.
On Thu, Dec 14, 2017 at 04:58:09AM -0800, Matthew Wilcox wrote: > On Wed, Dec 13, 2017 at 05:03:00PM -0800, Andrew Morton wrote: > > > sched/wait: assert the wait_queue_head lock is held in > > > __wake_up_common > > > > > > Better ensure we actually hold the lock using lockdep than just > > > commenting > > > on it. Due to the various exported _locked interfaces it is far too > > > easy > > > to get the locking wrong. > > > > I'm probably sitting on an older version. I've dropped > > > > epoll: use the waitqueue lock to protect ep->wq > > sched/wait: assert the wait_queue_head lock is held in __wake_up_common > > Looks pretty clear to me that userfaultfd is also abusing the wake_up_locked > interfaces: > > spin_lock(&ctx->fault_pending_wqh.lock); > __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range); > __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range); > spin_unlock(&ctx->fault_pending_wqh.lock); > > Sure, it's locked, but not by the lock you thought it was going to be. > > There doesn't actually appear to be a bug here; fault_wqh is always serialised > by fault_pending_wqh.lock, but lockdep can't know that. I think this patch > will solve the problem. > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index ac9a4e65ca49..a39bc3237b68 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -879,7 +879,7 @@ static int userfaultfd_release(struct inode *inode, > struct file *file) > */ > spin_lock(&ctx->fault_pending_wqh.lock); > __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range); > - __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range); > + __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range); > spin_unlock(&ctx->fault_pending_wqh.lock); > > /* Flush pending events that may still wait on event_wqh */ > @@ -1045,7 +1045,7 @@ static ssize_t userfaultfd_ctx_read(struct > userfaultfd_ctx *ctx, int no_wait, > * anyway. > */ > list_del(&uwq->wq.entry); > - __add_wait_queue(&ctx->fault_wqh, &uwq->wq); > + add_wait_queue(&ctx->fault_wqh, &uwq->wq); > > write_seqcount_end(&ctx->refile_seq); > > @@ -1194,7 +1194,7 @@ static void __wake_userfault(struct userfaultfd_ctx > *ctx, > __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, > range); > if (waitqueue_active(&ctx->fault_wqh)) > - __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range); > + __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range); > spin_unlock(&ctx->fault_pending_wqh.lock); > } > > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majord...@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"d...@kvack.org";> em...@kvack.org </a>
