POSIX Threads and dynamic memory allocation

I am using POSIX threads and in each thread, I allocated some data dynamically using the 'new' operator in C++. Also, I am using the standard template library. I am facing problems with the dynamic memory allocation part. My code keeps crashing randomly at places where I am allocating memory, deleting memory or manipulating string or other objects provided by the C++ STL. I tried finding out on the internet, but I can't find out for sure if functions like malloc() are thread-safe. I tried to backtrace using gdb and always, the trace ends with free() or malloc(). Sometimes I get a SIGSEGV and sometimes, I get a memory corruption error. What could be the problem?

If there is a function which I pass as an argument to pthread_create, then does the function need to be reentrant? Is it fine to allocate memory dynamically in the function?

Thanks.

have your read your man and google?
Is malloc() function provided in <stdlib.h> thread-safe? - comp.lang.c.moderated | Google Groups