linux-kernel - [PATCH 4.19] Ignore failure to unmap -1

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Message-Id: <20220708163750.2005-2-demi@invisiblethingslab.com>
Date:   Fri,  8 Jul 2022 12:37:45 -0400
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     Juergen Gross <jgross@...e.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Demi Marie Obenour <demi@...isiblethingslab.com>
Cc:     Linux kernel regressions <regressions@...ts.linux.dev>,
        stable@...r.kernel.org,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        Xen developer discussion <xen-devel@...ts.xenproject.org>
Subject: [PATCH 4.19] Ignore failure to unmap -1

The error paths of gntdev_mmap() can call unmap_grant_pages() even
though not all of the pages have been successfully mapped.  This will
trigger the WARN_ON()s in __unmap_grant_pages_done().  The number of
warnings can be very large; I have observed thousands of lines of
warnings in the systemd journal.

Avoid this problem by only warning on unmapping failure if the handle
being unmapped is not -1.  The handle field of any page that was not
successfully mapped will be -1, so this catches all cases wherr
unmapping can legitimately fail.

Suggested-by: Juergen Gross <jgross@...e.com>
Cc: stable@...r.kernel.org
Signed-off-by: Demi Marie Obenour <demi@...isiblethingslab.com>
Fixes: 73e9e72247b9 ("xen/gntdev: Avoid blocking in unmap_grant_pages()")
---
 drivers/xen/gntdev.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 492084814f55d8ed46d2d656db75b28a91dd7f06..27d955c5d9f9076266f77b9fedfa1a6a2ba08f56 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -416,7 +416,8 @@ static void __unmap_grant_pages_done(int result,
 	unsigned int offset = data->unmap_ops - map->unmap_ops;
 
 	for (i = 0; i < data->count; i++) {
-		WARN_ON(map->unmap_ops[offset+i].status);
+		WARN_ON(map->unmap_ops[offset+i].status &&
+			map->unmap_ops[offset+i].handle != -1);
 		pr_debug("unmap handle=%d st=%d\n",
 			map->unmap_ops[offset+i].handle,
 			map->unmap_ops[offset+i].status);
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab