linux-kernel - [RFC PATCH 5/5] userfaultfd_copy: return -ENOSPC in case mm has gone

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Date:   Tue, 24 Jan 2017 15:52:03 +0200
From:   Mike Rapoport <rppt@...ux.vnet.ibm.com>
To:     Linux-MM <linux-mm@...ck.org>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>
Subject: [RFC PATCH 5/5] userfaultfd_copy: return -ENOSPC in case mm has gone

In the non-cooperative userfaultfd case, the process exit may race with
outstanding mcopy_atomic called by the uffd monitor. Returning -ENOSPC
instead of -EINVAL when mm is already gone will allow uffd monitor to
distinguish this case from other error conditions.

Signed-off-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>
---
 fs/userfaultfd.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 839ffd5..6587f40 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1603,6 +1603,8 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
 		ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
 				   uffdio_copy.len);
 		mmput(ctx->mm);
+	} else {
+		return -ENOSPC;
 	}
 	if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
 		return -EFAULT;
-- 
1.9.1