userfaultfd: disable irqs when taking the waitqueue lock
diff mbox series

Message ID 20181018154101.18750-1-hch@lst.de
State New
Headers show
Series
  • userfaultfd: disable irqs when taking the waitqueue lock
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Commit Message

Christoph Hellwig Oct. 18, 2018, 3:41 p.m. UTC
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).

Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/userfaultfd.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Comments

Andrew Morton Oct. 18, 2018, 10:56 p.m. UTC | #1
On Thu, 18 Oct 2018 17:41:01 +0200 Christoph Hellwig <hch@lst.de> wrote:

> 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).

So...  this is needed in 4.19.x but not earlier?  Or something else?
Christoph Hellwig Oct. 19, 2018, 6:30 a.m. UTC | #2
On Thu, Oct 18, 2018 at 03:56:11PM -0700, Andrew Morton wrote:
> On Thu, 18 Oct 2018 17:41:01 +0200 Christoph Hellwig <hch@lst.de> wrote:
> 
> > 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).
> 
> So...  this is needed in 4.19.x but not earlier?  Or something else?

Yes.

Patch
diff mbox series

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index bfa0ec69f924..356d2b8568c1 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1026,7 +1026,7 @@  static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
 	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(struct userfaultfd_ctx *ctx, int no_wait,
 			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);