[Xen-changelog] [xen-4.2-testing] libxl: fix a variable underflow in libxl_wait_for_free_memory

[Xen patchbot-4.2-testing <patchbot@xxxxxxx>]

# HG changeset patch
# User Ronny Hegewald <ronny.hegewald@xxxxxxxxx>
# Date 1354208383 0
# Node ID 9e13427c023020756768c73217dab05295709fb3
# Parent  b3dafd42268af1ea9558b536702841625dd52500
libxl: fix a variable underflow in libxl_wait_for_free_memory

When xl is called to create a domU and there is not enough memory available,
then the autoballooning is called to extract memory from dom0. During the
ballooning a loop in libxl_wait_for_free_memory() waits unless enough memory
is available to create the domU.

But because of a variable-underflow the loop can finish too soon and xl
finally aborts with the message:

xc: error: panic: xc_dom_boot.c:161: xc_dom_boot_mem_init: can't allocate low 
memory for domain: Out of memory
libxl: error: libxl_dom.c:430:libxl__build_pv: xc_dom_boot_mem_init failed: 
Device or resource busy
libxl: error: libxl_create.c:901:domcreate_rebuild_done: cannot (re-)build 
domain: -3

The variable-underflow happens when freemem_slack is larger then
info.free_pages*4, because the solution of this operation is converted
implicit to a unsigned int to match the type of memory_kb.

Add a extra check for this condition to solve the problem.

Signed-off-by: Ronny Hegewald <Ronny.Hegewald@xxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Committed-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

xen-unstable changeset: 26190:678718a2e565
Backport-requested-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
Committed-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---


diff -r b3dafd42268a -r 9e13427c0230 tools/libxl/libxl.c
--- a/tools/libxl/libxl.c       Thu Nov 29 16:07:55 2012 +0000
+++ b/tools/libxl/libxl.c       Thu Nov 29 16:59:43 2012 +0000
@@ -3592,7 +3592,8 @@ int libxl_wait_for_free_memory(libxl_ctx
         rc = libxl_get_physinfo(ctx, &info);
         if (rc < 0)
             goto out;
-        if (info.free_pages * 4 - freemem_slack >= memory_kb) {
+        if (info.free_pages * 4 >= freemem_slack &&
+            info.free_pages * 4 - freemem_slack >= memory_kb) {
             rc = 0;
             goto out;
         }

_______________________________________________
Xen-changelog mailing list
Xen-changelog@xxxxxxxxxxxxx
http://lists.xensource.com/xen-changelog