Rich Felker
de7e99c585
when manipulating the robust list, the order of stores matters, because the code may be asynchronously interrupted by a fatal signal and the kernel will then access the robust list in what is essentially an async-signal context. previously, aliasing considerations made it seem unlikely that a compiler could reorder the stores, but proving that they could not be reordered incorrectly would have been extremely difficult. instead I've opted to make all the pointers used as part of the robust list, including those in the robust list head and in the individual mutexes, volatile. in addition, the format of the robust list has been changed to point back to the head at the end, rather than ending with a null pointer. this is to match the documented kernel robust list ABI. the null pointer, which was previously used, only worked because faults during access terminate the robust list processing.
39 lines
1013 B
C
39 lines
1013 B
C
#include "pthread_impl.h"
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void __vm_lock_impl(int);
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void __vm_unlock_impl(void);
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int pthread_mutex_unlock(pthread_mutex_t *m)
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{
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pthread_t self;
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int waiters = m->_m_waiters;
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int cont;
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int type = m->_m_type & 15;
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int priv = (m->_m_type & 128) ^ 128;
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if (type != PTHREAD_MUTEX_NORMAL) {
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self = __pthread_self();
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if ((m->_m_lock&0x7fffffff) != self->tid)
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return EPERM;
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if ((type&3) == PTHREAD_MUTEX_RECURSIVE && m->_m_count)
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return m->_m_count--, 0;
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if (!priv) {
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self->robust_list.pending = &m->_m_next;
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__vm_lock_impl(+1);
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}
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volatile void *prev = m->_m_prev;
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volatile void *next = m->_m_next;
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*(volatile void *volatile *)prev = next;
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if (next != &self->robust_list.head) *(volatile void *volatile *)
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((char *)next - sizeof(void *)) = prev;
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}
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cont = a_swap(&m->_m_lock, (type & 8) ? 0x40000000 : 0);
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if (type != PTHREAD_MUTEX_NORMAL && !priv) {
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self->robust_list.pending = 0;
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__vm_unlock_impl();
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}
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if (waiters || cont<0)
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__wake(&m->_m_lock, 1, priv);
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return 0;
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}
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