Re: libmalloc: forget to free something in nano_try_madvise in nano_malloc?
Re: libmalloc: forget to free something in nano_try_madvise in nano_malloc?
- Subject: Re: libmalloc: forget to free something in nano_try_madvise in nano_malloc?
- From: Greg Parker <email@hidden>
- Date: Mon, 05 Jan 2015 13:35:02 -0800
> On Dec 23, 2014, at 12:22 AM, cee1 <email@hidden> wrote:
>
> Hi all,
>
> I'm interesting to the internal of malloc in OS X and learning some
> code snippets of it, and I find it seems forget to free page_bitarray
> in nano_try_madvise()
> (http://www.opensource.apple.com/source/libmalloc/libmalloc-53.1.1/src/nano_malloc.c,
> line 1395):
>
> """
> bitarray_t slot_bitarray = bitarray_create(log_size);
> bitarray_t page_bitarray = bitarray_create(log_page_count);
>
> if (!slot_bitarray) {
> /******* Shouldn't we free(page_bitarray) here？*******/
> return bytes_toward_goal;
> }
>
> if (!page_bitarray) {
> free(slot_bitarray);
> return bytes_toward_goal;
> }
> """
Your analysis looks correct to me. You should file a bug report.
In practice this should not be a serious problem. A process that fails to allocate a bit array is almost certainly going to die very soon due to other out-of-memory failures.
> BTW, in segregated_band_grow(), does it miss an unmap call if return
> another vm area that's not what asked for?
>
> """
> kern_return_t kr = mach_vm_map(mach_task_self(), &vm_addr, BAND_SIZE,
> 0, VM_MAKE_TAG(VM_MEMORY_MALLOC_NANO),
> MEMORY_OBJECT_NULL, 0, FALSE,
> VM_PROT_DEFAULT, VM_PROT_ALL, VM_INHERIT_DEFAULT);
>
> void *q = (uintptr_t)vm_addr;
> if (kr || q != (void *)(p & ~((uintptr_t)(BAND_SIZE - 1)))) //
> Must get exactly what we asked for
> return FALSE;
>
> """
mach_vm_map() with that set of parameters is not allowed to return an address that is not the requested address. That part of the check will never fail unless there is a bug in mach_vm_map(). It would make sense to rearrange or annotate the code to clarify the check, but it should never result in a memory leak.
--
Greg Parker email@hidden Runtime Wrangler
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