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.
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@ -323,23 +323,15 @@ void *rt_mp_alloc(rt_mp_t mp, rt_int32_t time)
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rt_uint8_t *block_ptr;
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register rt_base_t level;
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struct rt_thread *thread;
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rt_uint32_t before_sleep = 0;
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/* get current thread */
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thread = rt_thread_self();
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/* disable interrupt */
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level = rt_hw_interrupt_disable();
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if (mp->block_free_count)
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{
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/* memory block is available. decrease the free block counter */
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mp->block_free_count --;
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/* get block from block list */
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block_ptr = mp->block_list;
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mp->block_list = *(rt_uint8_t **)block_ptr;
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/* point to memory pool */
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*(rt_uint8_t **)block_ptr = (rt_uint8_t *)mp;
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}
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else
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while (mp->block_free_count == 0)
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{
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/* memory block is unavailable. */
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if (time == 0)
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@ -347,24 +339,25 @@ void *rt_mp_alloc(rt_mp_t mp, rt_int32_t time)
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/* enable interrupt */
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rt_hw_interrupt_enable(level);
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rt_set_errno(-RT_ETIMEOUT);
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return RT_NULL;
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}
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else
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{
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RT_DEBUG_NOT_IN_INTERRUPT;
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/* get current thread */
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thread = rt_thread_self();
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RT_DEBUG_NOT_IN_INTERRUPT;
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thread->error = RT_EOK;
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/* need suspend thread */
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rt_thread_suspend(thread);
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rt_list_insert_after(&(mp->suspend_thread), &(thread->tlist));
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mp->suspend_thread_count ++;
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mp->suspend_thread_count++;
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if (time > 0)
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{
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/* get the start tick of timer */
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before_sleep = rt_tick_get();
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/* init thread timer and start it */
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rt_timer_control(&(thread->thread_timer),
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RT_TIMER_CTRL_SET_TIME,
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@ -381,20 +374,28 @@ void *rt_mp_alloc(rt_mp_t mp, rt_int32_t time)
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if (thread->error != RT_EOK)
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return RT_NULL;
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if (time > 0)
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{
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time -= rt_tick_get() - before_sleep;
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if (time < 0)
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time = 0;
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}
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/* disable interrupt */
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level = rt_hw_interrupt_disable();
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}
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/* decrease free block */
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mp->block_free_count --;
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/* memory block is available. decrease the free block counter */
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mp->block_free_count--;
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/* get block from block list */
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block_ptr = mp->block_list;
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RT_ASSERT(block_ptr != RT_NULL);
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/* Setup the next free node. */
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mp->block_list = *(rt_uint8_t **)block_ptr;
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/* point to memory pool */
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*(rt_uint8_t **)block_ptr = (rt_uint8_t *)mp;
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}
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}
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/* enable interrupt */
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rt_hw_interrupt_enable(level);
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