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This commit is contained in:
Gregory Nutt 2018-12-27 09:32:47 -06:00
parent 0cd5a232ea
commit 86224f9b7e
1 changed files with 37 additions and 16 deletions
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53
mm/mm_heap/mm_sem.c
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@ -140,22 +140,39 @@ int mm_trysemaphore(FAR struct mm_heap_s *heap)
int ret;
/* sched_self() returns the TCB at the head of the ready-to-run list.
* mm_trysemaphore() is an intimate component of the memory garbage
* collection logic and, hence, may be called in many different contexts.
* mm_trysemaphore() may be called during context switches. There are
* certain situations during context switching when the the OS data
* structures are in flux and where the current task (i.e., the task at
* the head of the ready-to-run task list) is not actually running.
* Granting the semaphore access in that case is known to result in heap
* corruption as in the following failure scenario.
*
* It may be called during context switches for example. There are certain
* conditions when the the OS data structures are in flux and where the
* task at the head of the ready-to-run task list is not actually running.
* Granting the semaphore access in this case is known to result in heap
* corruption and must be avoided.
* ---------------------------- -------------------------------
* TASK A TASK B
* ---------------------------- -------------------------------
* Begins memory allocation.
* - Holder is set to TASK B
* <---- Task B preempted, Task A runs
* Task A exits
* - Current task set to Task B
* Free tcb and stack memory
* - Since holder is Task B,
* memory manager is re-
* entered, and
* - Heap is corrupted.
* ---------------------------- -------------------------------
*/
/* Do I already have the semaphore? */
/* Does the current task already hold the semaphore? Is the current
* task actually running?
*/
my_pid = rtcb->pid;
if (heap->mm_holder == my_pid && rtcb->task_state == TSTATE_TASK_RUNNING)
{
/* Yes, just increment the number of references that I have */
/* Yes, just increment the number of references held by the current
* task.
*/
heap->mm_counts_held++;
ret = OK;
@ -171,7 +188,7 @@ int mm_trysemaphore(FAR struct mm_heap_s *heap)
goto errout;
}
/* We have it. Claim the heap and return */
/* We have it. Claim the heap for the current task and return */
heap->mm_holder = my_pid;
heap->mm_counts_held = 1;
@ -201,11 +218,13 @@ void mm_takesemaphore(FAR struct mm_heap_s *heap)
#endif
pid_t my_pid = getpid();
/* Do I already have the semaphore? */
/* Does the current task already hold the semaphore? */
if (heap->mm_holder == my_pid)
{
/* Yes, just increment the number of references that I have */
/* Yes, just increment the number of references held by the current
* task.
*/
heap->mm_counts_held++;
}
@ -238,7 +257,7 @@ void mm_takesemaphore(FAR struct mm_heap_s *heap)
while (ret == -EINTR);
/* We have it (or some awful, unexpected error occurred). Claim
* the semaphore and return.
* the semaphore for the current task and return.
*/
heap->mm_holder = my_pid;
@ -269,11 +288,13 @@ void mm_givesemaphore(FAR struct mm_heap_s *heap)
pid_t my_pid = getpid();
#endif
/* I better be holding at least one reference to the semaphore */
/* The current task should be holding at least one reference to the
* semaphore.
*/
DEBUGASSERT(heap->mm_holder == my_pid);
/* Do I hold multiple references to the semaphore */
/* Does the current task hold multiple references to the semaphore */
if (heap->mm_counts_held > 1)
{
@ -285,7 +306,7 @@ void mm_givesemaphore(FAR struct mm_heap_s *heap)
}
else
{
/* Nope, this is the last reference I have */
/* Nope, this is the last reference held by the current task. */
mseminfo("PID=%d giving\n", my_pid);