[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] libxl - fix a variable underflow in libxl_wait_for_free_memory
On Fri, 2012-11-23 at 00:14 +0000, Ronny Hegewald wrote: > 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. > > The problem is fixed by a proper casting. Thanks for your patch. I think the correct fix is to check for the "freemem_slack > info.free_pages * 4" case explicitly rather than relying on casts. Ian. > > > Signed-off-by: Ronny Hegewald <Ronny.Hegewald@xxxxxxxxx> > > --- xen-4.3-20121121/tools/libxl/libxl.c.org 2012-11-22 03:34:00.000000000 > +0000 > +++ xen-4.3-20121121/tools/libxl/libxl.c 2012-11-22 03:34:47.000000000 > +0000 > @@ -3763,7 +3763,7 @@ 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 ((int64_t)(info.free_pages * 4 - freemem_slack) >= memory_kb) { > rc = 0; > goto out; > } > > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxx > http://lists.xen.org/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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