The kernel facility named kmemleak is very useful in tracking memory leaks in
the kernel. Unfortunately, there are instances when the scan of allocated memory
cannot find an active user even though one actually exists. In this case,
kmemleak issues a false positive result. This situation is verified by unloading
the driver in question and noting that the leak then disappears.
Unfortunately, vboxdrv displays such false positives. A typical traceback is
unreferenced object 0xffff88020cfeb080 (size 128):
comm "EMT-0", pid 4180, jiffies 4297724945 (age 80.264s)
hex dump (first 32 bytes):
19 01 09 18 01 00 00 80 58 00 00 00 58 00 00 00 ........X...X...
10 12 61 19 58 00 00 00 03 00 00 00 00 00 00 00 ..a.X...........
backtrace:
[<ffffffff8169ef8a>] kmemleak_alloc+0x4a/0xa0
[<ffffffff811e6d94>] __kmalloc+0xe4/0x230
[<ffffffffa0940dd8>] rtR0MemAllocEx+0x178/0x230 [vboxdrv]
[<ffffffffa093ec1b>] VBoxHost_RTMemAllocZTag+0x1b/0x40 [vboxdrv]
[<ffffffffa0940017>] rtR0MemObjNew+0x37/0x70 [vboxdrv]
[<ffffffffa09410c8>] rtR0MemObjLinuxAllocPages+0x48/0x200 [vboxdrv]
[<ffffffffa0941948>] rtR0MemObjNativeAllocCont+0x48/0xe0 [vboxdrv]
[<ffffffffa093f5f4>] VBoxHost_RTR0MemObjAllocContTag+0x54/0x70 [vboxdrv]
[<ffffffffffffffff>] 0xffffffffffffffff
Fortunately, these false positives are easily quieted one they have been
identified. The following two-line patch, which has an MIT license, does the trick:
Index: VirtualBox-5.1.4/src/VBox/Runtime/r0drv/linux/alloc-r0drv-linux.c
===================================================================
--- VirtualBox-5.1.4.orig/src/VBox/Runtime/r0drv/linux/alloc-r0drv-linux.c
+++ VirtualBox-5.1.4/src/VBox/Runtime/r0drv/linux/alloc-r0drv-linux.c
@@ -35,7 +35,7 @@
#include <iprt/assert.h>
#include <iprt/err.h>
#include "r0drv/alloc-r0drv.h"
-
+#include <linux/kmemleak.h>
#if (defined(RT_ARCH_AMD64) || defined(DOXYGEN_RUNNING)) &&
!defined(RTMEMALLOC_EXEC_HEAP)
# if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 23)
@@ -294,6 +294,7 @@ DECLHIDDEN(int) rtR0MemAllocEx(size_t cb
fFlags &= ~RTMEMHDR_FLAG_KMALLOC;
pHdr = vmalloc(cb + sizeof(*pHdr));
}
+ kmemleak_not_leak(pHdr);
}
else
pHdr = vmalloc(cb + sizeof(*pHdr));
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