From: Christoph Hellwig hch@lst.de Subject: userfaultfd: disable irqs when taking the waitqueue lock

userfaultfd contains howe-grown locking of the waitqueue lock, and does not disable interrupts. This relies on the fact that no one else takes it from interrupt context and violates an invariat of the normal waitqueue locking scheme. With aio poll it is easy to trigger other locks that disable interrupts (or are called from interrupt context).

Link: http://lkml.kernel.org/r/20181018154101.18750-1-hch@lst.de Signed-off-by: Christoph Hellwig hch@lst.de Reviewed-by: Andrea Arcangeli aarcange@redhat.com Reviewed-by: Andrew Morton akpm@linux-foundation.org Cc: stable@vger.kernel.org [4.19.x] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/userfaultfd.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/fs/userfaultfd.c~userfaultfd-disable-irqs-when-taking-the-waitqueue-lock +++ a/fs/userfaultfd.c @@ -1026,7 +1026,7 @@ static ssize_t userfaultfd_ctx_read(stru struct userfaultfd_ctx *fork_nctx = NULL;

/* always take the fd_wqh lock before the fault_pending_wqh lock */ - spin_lock(&ctx->fd_wqh.lock); + spin_lock_irq(&ctx->fd_wqh.lock); __add_wait_queue(&ctx->fd_wqh, &wait); for (;;) { set_current_state(TASK_INTERRUPTIBLE); @@ -1112,13 +1112,13 @@ static ssize_t userfaultfd_ctx_read(stru ret = -EAGAIN; break; } - spin_unlock(&ctx->fd_wqh.lock); + spin_unlock_irq(&ctx->fd_wqh.lock); schedule(); - spin_lock(&ctx->fd_wqh.lock); + spin_lock_irq(&ctx->fd_wqh.lock); } __remove_wait_queue(&ctx->fd_wqh, &wait); __set_current_state(TASK_RUNNING); - spin_unlock(&ctx->fd_wqh.lock); + spin_unlock_irq(&ctx->fd_wqh.lock);

if (!ret && msg->event == UFFD_EVENT_FORK) { ret = resolve_userfault_fork(ctx, fork_nctx, msg); _