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fix race condition in List_insert 

Revert mx parameter and mutex lock while operating the list.
Mutex was removed with 94d24160 informing that:
'Use InterlockedCompareExchangePointer to ensure race safeness
without using a mutex.'

But it does not.

Calling pthread_mutex_init and pthread_mutex_destroy from two or
more threads occasionally leads to hang in pthread_mutex_destroy.

To not change the behaviour of other cases where List_insert was called,
List_insert_nolock is added.
This commit is contained in:
Aleksand Malikov 2021-08-23 17:27:48 +03:00 committed by Corinna Vinschen
parent bc0e8a9961
commit 1a821390d1
2 changed files with 19 additions and 6 deletions
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8
winsup/cygwin/thread.cc
View File

@ -1595,7 +1595,7 @@ pthread_rwlock::add_reader ()
{ {
RWLOCK_READER *rd = new RWLOCK_READER; RWLOCK_READER *rd = new RWLOCK_READER;
if (rd) if (rd)
List_insert (readers, rd); List_insert_nolock (readers, rd);
return rd; return rd;
} }
@ -2165,7 +2165,7 @@ pthread::atfork (void (*prepare)(void), void (*parent)(void), void (*child)(void
if (prepcb) if (prepcb)
{ {
prepcb->cb = prepare; prepcb->cb = prepare;
List_insert (MT_INTERFACE->pthread_prepare, prepcb); List_insert_nolock (MT_INTERFACE->pthread_prepare, prepcb);
} }
if (parentcb) if (parentcb)
{ {
@ -2174,7 +2174,7 @@ pthread::atfork (void (*prepare)(void), void (*parent)(void), void (*child)(void
while (*t) while (*t)
t = &(*t)->next; t = &(*t)->next;
/* t = pointer to last next in the list */ /* t = pointer to last next in the list */
List_insert (*t, parentcb); List_insert_nolock (*t, parentcb);
} }
if (childcb) if (childcb)
{ {
@ -2183,7 +2183,7 @@ pthread::atfork (void (*prepare)(void), void (*parent)(void), void (*child)(void
while (*t) while (*t)
t = &(*t)->next; t = &(*t)->next;
/* t = pointer to last next in the list */ /* t = pointer to last next in the list */
List_insert (*t, childcb); List_insert_nolock (*t, childcb);
} }
return 0; return 0;
} }

17
winsup/cygwin/thread.h
View File

@ -111,7 +111,20 @@ typedef enum
} verifyable_object_state; } verifyable_object_state;
template <class list_node> inline void template <class list_node> inline void
List_insert (list_node *&head, list_node *node) List_insert (fast_mutex &mx, list_node *&head, list_node *node)
{
if (!node)
return;
mx.lock ();
do
node->next = head;
while (InterlockedCompareExchangePointer ((PVOID volatile *) &head,
node, node->next) != node->next);
mx.unlock ();
}
template <class list_node> inline void
List_insert_nolock (list_node *&head, list_node *node)
{ {
if (!node) if (!node)
return; return;
@ -163,7 +176,7 @@ template <class list_node> class List
void insert (list_node *node) void insert (list_node *node)
{ {
List_insert (head, node); List_insert (mx, head, node);
} }
void remove (list_node *node) void remove (list_node *node)