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kernel: mempool: fix race condition in rt_mp_alloc 

When thread wake up from waiting for memory, there is a chance that
there is no memory available in high pressure. So use a loop to check
again. Otherwise, there will be a NULL reference.
This commit is contained in:
Grissiom 2014-08-20 10:16:04 +08:00
parent 0135dd38cf
commit b8bf6bef76
1 changed files with 56 additions and 55 deletions
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111
src/mempool.c
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@ -323,23 +323,15 @@ void *rt_mp_alloc(rt_mp_t mp, rt_int32_t time)
rt_uint8_t *block_ptr;
register rt_base_t level;
struct rt_thread *thread;
rt_uint32_t before_sleep = 0;
/* get current thread */
thread = rt_thread_self();
/* disable interrupt */
level = rt_hw_interrupt_disable();
if (mp->block_free_count)
{
/* memory block is available. decrease the free block counter */
mp->block_free_count --;
/* get block from block list */
block_ptr = mp->block_list;
mp->block_list = *(rt_uint8_t **)block_ptr;
/* point to memory pool */
*(rt_uint8_t **)block_ptr = (rt_uint8_t *)mp;
}
else
while (mp->block_free_count == 0)
{
/* memory block is unavailable. */
if (time == 0)
@ -347,55 +339,64 @@ void *rt_mp_alloc(rt_mp_t mp, rt_int32_t time)
/* enable interrupt */
rt_hw_interrupt_enable(level);
rt_set_errno(-RT_ETIMEOUT);
return RT_NULL;
}
else
RT_DEBUG_NOT_IN_INTERRUPT;
thread->error = RT_EOK;
/* need suspend thread */
rt_thread_suspend(thread);
rt_list_insert_after(&(mp->suspend_thread), &(thread->tlist));
mp->suspend_thread_count++;
if (time > 0)
{
RT_DEBUG_NOT_IN_INTERRUPT;
/* get the start tick of timer */
before_sleep = rt_tick_get();
/* get current thread */
thread = rt_thread_self();
thread->error = RT_EOK;
/* need suspend thread */
rt_thread_suspend(thread);
rt_list_insert_after(&(mp->suspend_thread), &(thread->tlist));
mp->suspend_thread_count ++;
if (time > 0)
{
/* init thread timer and start it */
rt_timer_control(&(thread->thread_timer),
RT_TIMER_CTRL_SET_TIME,
&time);
rt_timer_start(&(thread->thread_timer));
}
/* enable interrupt */
rt_hw_interrupt_enable(level);
/* do a schedule */
rt_schedule();
if (thread->error != RT_EOK)
return RT_NULL;
/* disable interrupt */
level = rt_hw_interrupt_disable();
/* decrease free block */
mp->block_free_count --;
/* get block from block list */
block_ptr = mp->block_list;
mp->block_list = *(rt_uint8_t **)block_ptr;
/* point to memory pool */
*(rt_uint8_t **)block_ptr = (rt_uint8_t *)mp;
/* init thread timer and start it */
rt_timer_control(&(thread->thread_timer),
RT_TIMER_CTRL_SET_TIME,
&time);
rt_timer_start(&(thread->thread_timer));
}
/* enable interrupt */
rt_hw_interrupt_enable(level);
/* do a schedule */
rt_schedule();
if (thread->error != RT_EOK)
return RT_NULL;
if (time > 0)
{
time -= rt_tick_get() - before_sleep;
if (time < 0)
time = 0;
}
/* disable interrupt */
level = rt_hw_interrupt_disable();
}
/* memory block is available. decrease the free block counter */
mp->block_free_count--;
/* get block from block list */
block_ptr = mp->block_list;
RT_ASSERT(block_ptr != RT_NULL);
/* Setup the next free node. */
mp->block_list = *(rt_uint8_t **)block_ptr;
/* point to memory pool */
*(rt_uint8_t **)block_ptr = (rt_uint8_t *)mp;
/* enable interrupt */
rt_hw_interrupt_enable(level);