linux-kernel - [PATCH] userfaultfd: replace ENOSPC with ESRCH in case mm has gone during copy/zeropage

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Date:   Mon,  7 Aug 2017 16:12:25 +0300
From:   Mike Rapoport <rppt@...ux.vnet.ibm.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm <linux-mm@...ck.org>, lkml <linux-kernel@...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>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH] userfaultfd: replace ENOSPC with ESRCH in case mm has gone during copy/zeropage

When the process exit races with outstanding mcopy_atomic, it would be
better to return ESRCH error. When such race occurs the process and it's mm
are going away and returning "no such process" to the uffd monitor seems
better fit than ENOSPC.

Suggested-by: Michal Hocko <mhocko@...e.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@...hat.com>
Cc: Pavel Emelyanov <xemul@...tuozzo.com>
Cc: Mike Kravetz <mike.kravetz@...cle.com>
Signed-off-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>
---
The man-pages update is ready and I'll send it out once the patch is
merged.

 fs/userfaultfd.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 06ea26b8c996..b0d5897bc4e6 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1600,7 +1600,7 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
 				   uffdio_copy.len);
 		mmput(ctx->mm);
 	} else {
-		return -ENOSPC;
+		return -ESRCH;
 	}
 	if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
 		return -EFAULT;
@@ -1647,7 +1647,7 @@ static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
 				     uffdio_zeropage.range.len);
 		mmput(ctx->mm);
 	} else {
-		return -ENOSPC;
+		return -ESRCH;
 	}
 	if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
 		return -EFAULT;
-- 
2.7.4