On Mon, May 22, 2017 at 11:19:08AM -0700, Andy Lutomirski wrote: > On Mon, May 22, 2017 at 10:35 AM, Catalin Marinas > <catalin.marinas@xxxxxxx> wrote: > > Kmemleak requires that vmalloc'ed objects have a minimum reference count > > of 2: one in the corresponding vm_struct object and the other owned by > > the vmalloc() caller. There are cases, however, where the original > > vmalloc() returned pointer is lost and, instead, a pointer to vm_struct > > is stored (see free_thread_stack()). Kmemleak currently reports such > > objects as leaks. > > > > This patch adds support for treating any surplus references to an object > > as additional references to a specified object. It introduces the > > kmemleak_vmalloc() API function which takes a vm_struct pointer and sets > > its surplus reference passing to the actual vmalloc() returned pointer. > > The __vmalloc_node_range() calling site has been modified accordingly. > > > > An unrelated minor change is included in this patch to change the type > > of kmemleak_object.flags to unsigned int (previously unsigned long). > > > > Reported-by: "Luis R. Rodriguez" <mcgrof@xxxxxxxxxx> > > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > > Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> > > Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx> > > --- > > > > As per [1], I added support to use pointers to vm_struct as an > > alternative way to avoid false positives when the original vmalloc() > > pointer has been lost. This is slightly harder to reason about but it > > seems to work for this use-case. I'm not aware of other cases (than > > free_thread_stack()) where the original vmalloc() pointer is removed in > > favour of a vm_struct one. > > > > An alternative implementation (simpler to understand), if preferred, is > > to annotate alloc_thread_stack_node() and free_thread_stack() with > > kmemleak_unignore()/kmemleak_ignore() calls and proper comments. > > > > I personally prefer the option in this patch. It keeps the special > case in kmemleak and the allocation code rather than putting it in the > consumer code. > > Also, I want to add an API at some point that vmallocs some memory and > returns the vm_struct directly. That won't work with explicit > annotations in the caller because kmemleak might think it's leaked > before the caller can execute the annotations. While kmemleak delays the reporting of newly allocated objects to avoid such race, we need to keep annotations to a minimum anyway (only for special cases, definitely not for each caller of an allocation API). The proposed kmemleak_vmalloc() API in this patch would cover your case without any additional annotation. -- Catalin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
