[PATCH v2] malloc: Prevent arena free_list from turning cyclic [BZ #19048]

[Florian Weimer]

On 10/09/2015 08:28 PM, Siddhesh Poyarekar wrote:
> The only time a thread ever switches arenas is when it fails to allocate
> on the earlier arena.  Also, what's hidden in the implementation is that
> the switch always happens from the main arena to a non-main arena and
> never in any other condition.  So you could consolidate the replacement
> logic to just arena_get2 where you do tsd_setspecific (arena_key, NULL)
> if avoid_arena is set and decrement the refcount on avoid_arena.
> There's no other place where you want to detach from an arena.
> 
> It makes no sense to stick to the avoided arena anyway because we failed
> to allocate on that arena and if we don't find another arena either
> through a free list or reused_arena, we will try mmap and if even that
> fails, we fail allocation.

Thanks for your comments.  The code is difficult to follow (and it does
not seem to do what some people expect it to do, it seems).  But I do
not want to refactor it in a major way right now.

I believe I have addressed your comments in the attached patch.  I would
really like to have a review of the pthread_atfork changes because these
bits are really tricky.

Florian
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