mm: ashmem: fix deadlock when system is low on memory When system is low on memory, allocating memory while holding the ashmem_mutex may try to directly reclaim memory. Then ashmem_shrink() is called in same thread. It will deadlock at acquiring ashmem_mutex. This change lets ashmem_shrink() return failure if ashmem_mutex is not available. Memory will be reclaimed from others.

Change-Id: I3b6024d5477d37245f4ebde6d7069fb77af789ee
Signed-off-by: Yuanyuan Zhong <yuanyuan.zhong@gmail.com>
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