Re: Memory leak in bitmap code?

[Stefan Hajnoczi]

On Mon, Jul 20, 2020 at 10:50:23AM +0300, Vladimir Sementsov-Ogievskiy wrote:
> 20.07.2020 09:16, Thomas Huth wrote:
> > 
> >   Hi,
> > 
> > looks like the LeakSanitizer spotted a memory leak in the bitmap related
> > code ... not sure why it just triggered with Richard's pull request, and
> > I can also not reproduce it... But since there is a nice backtrace in it
> > and there have been some bitmap-related patches recently, could you
> > maybe have a look whether this rings a bell by any chance:
> > 
> >   https://gitlab.com/qemu-project/qemu/-/jobs/645799805#L3282
> > 
> 
> Hi! Hmm. bitmap.c/bitmap.h is a simple bitmap library, which was not changed 
> this
> year. The last commit I see is about a year ago.
> 
> So, I assume the problem should be somewhere below in the stack trace.
> 
> I don't know this code, but try to look at:
> 
> OK, sanitizer reports that we loose the memory allocated at exce.c:2219, i.e.
> 
> new_blocks->blocks1[j] = bitmap_new(DIRTY_MEMORY_BLOCK_SIZE);
> 
> Hmm. And where is this bitmap released? I can't find the place. May be the 
> leak
> was introduced in far 5b82b703b69acc67b7 with this bitmap_new()? Add Stefan to
> CC.

g_free_rcu() is used when ram_list->dirty_memory[] is extended, so the
leak is not dangerous.

There is no cleanup function for the global ram_list. I'll investigate
writing a patch to clean up ram_list fields.

Thanks,
Stefan

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