linux-kernel - [PATCH 4.12 021/106] userfaultfd: non-cooperative: flush event

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Date:   Wed,  9 Aug 2017 09:52:05 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.12 021/106] userfaultfd: non-cooperative: flush event_wqh at release time

4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mike Rapoport <rppt@...ux.vnet.ibm.com>

commit 5a18b64e3f02125be1c0ef777501ae38aafe2a24 upstream.

There may still be threads waiting on event_wqh at the time the
userfault file descriptor is closed.  Flush the events wait-queue to
prevent waiting threads from hanging.

Link: http://lkml.kernel.org/r/1501398127-30419-1-git-send-email-rppt@linux.vnet.ibm.com
Fixes: 9cd75c3cd4c3d ("userfaultfd: non-cooperative: add ability to report
non-PF events from uffd descriptor")
Signed-off-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@...hat.com>
Cc: Pavel Emelyanov <xemul@...tuozzo.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/userfaultfd.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -851,6 +851,9 @@ wakeup:
 	__wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range);
 	spin_unlock(&ctx->fault_pending_wqh.lock);

+	/* Flush pending events that may still wait on event_wqh */
+	wake_up_all(&ctx->event_wqh);
+
 	wake_up_poll(&ctx->fd_wqh, POLLHUP);
 	userfaultfd_ctx_put(ctx);
 	return 0;