ossl.c: make legacy locking callbacks reentrant #155
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In preparation for making the mutexes reentrant. It is common to the non-dynamic and the dynamic locking callbacks.
Although it's not documented explicitly that the locking callbacks must provide reentrant mutexes, it seems to be required. Specifically, the session_remove_cb callback function of an SSL_CTX is called in a critical section for CRYPTO_LOCK_SSL_CTX, which is shared across the library. This leads, if the callback function calls another OpenSSL function that will attempt to lock CRYPTO_LOCK_SSL_CTX, to deadlock. SSL_CTX_free() is one example of such a function. http://ci.rvm.jp/results/trunk@P895/64001
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Although it's not documented explicitly that the locking callbacks must
provide reentrant mutexes, it seems to be required.
Specifically, the session_remove_cb callback function of an SSL_CTX is
called in a critical section for CRYPTO_LOCK_SSL_CTX, which is shared
across the library. This leads, if the callback function calls another
OpenSSL function that will attempt to lock CRYPTO_LOCK_SSL_CTX, to
deadlock. SSL_CTX_free() is one example of such a function.
http://ci.rvm.jp/results/trunk@P895/64001