[PATCH 4/5] Fix deadlock in _int_free consistency check

[Florian Weimer]

On 10/12/2017 12:18 PM, Wilco Dijkstra wrote:
> Florian Weimer wrote:
>      
>> I don't think the subject line is correct.  What is the deadlock?  I
>> don't see it.
> 
>> -	if (!have_lock
>> -	    || ({ __libc_lock_lock (av->mutex);
> 
> It's right there. Have_lock means you've just done __libc_lock_lock (av->mutex),
> so doing it again (same thread) implies deadlock.

Hmm.

So if we enter this code path with have_lock, we don't have to re-do the 
check, but malloc_printerr will be called in the end anyway, so this is 
not the interesting case.

In practice, without heap corruption, the lock will be acquired here and 
re-checking is needed, so I think your cleanup is okay after all.  The 
logic is indeed much clearer.

Thanks,
Florian