回复:回复:[Zephyr-devel] Is this a bug? how to guarantee the "atomic semantics access of readyqueue" in "do_swap" function during context switch in SMP mode?


"曹子龙
 

hi :
would the "wait_for_switch(new_thread)" would aggravate the race condition not fix the race condition?
 
the old thread save state still cant guarantee to be saved before it pick up by other cpus to run ????


曹子龙

珠海全志科技股份有限公司      BU1-PSW

地址:广东省珠海市高新区唐家湾镇科技2路9号

TEL:13824125580

Email:caozilong@...

网址: http://www.allwinnertech.com

 


------------------------------------------------------------------
发件人:Williams, Jennifer M <jennifer.m.williams@...>
发送时间:2020年1月23日(星期四) 02:43
收件人:曹子龙 <caozilong@...>; "Ross, Andrew J" <andrew.j.ross@...>; devel <devel@...>
主 题:RE: 回复:[Zephyr-devel] Is this a bug? how to guarantee the "atomic semantics access of readyqueue" in "do_swap" function during context switch in SMP mode?

Hi

The PR mentioned below (https://github.com/zephyrproject-rtos/zephyr/pull/21903) was merged yesterday – please review the comments and code changes for more details on the fix. Can you please describe a bit more how your potential issue is not addressed by this PR?

 

Thank you,

Jen

 

From: devel@... <devel@...> On Behalf Of "???
Sent: Tuesday, January 21, 2020 10:31 PM
To: Ross, Andrew J <andrew.j.ross@...>; devel <devel@...>
Subject: 回复:[Zephyr-devel] Is this a bug? how to guarantee the "atomic semantics access of readyqueue" in "do_swap" function during context switch in SMP mode?

 

Hi andy:

 

     so, this is turely a issue that i have illustrated in last emai? is that true?

so the mainline code still has this issue, right?

 

 thank you.

 

 

曹子

珠海全志科技股份有限公司      BU1-PSW

地址:广东省珠海市高新区唐家湾镇科技2路9号

TEL:13824125580

Email:caozilong@...

网址: http://www.allwinnertech.com

 

 

------------------------------------------------------------------

发件人:Andy Ross <andrew.j.ross@...>

发送时间:2020121(星期二) 22:45

收件人:曹子 <caozilong@...>; devel <devel@...>

主 题:Re: [Zephyr-devel] Is this a bug? how to guarantee the "atomic semantics access of readyqueue" in "do_swap" function during context switch in SMP mode?

 

There is a fix for exactly this race this in https://github.com/zephyrproject-rtos/zephyr/pull/21903

On 1/21/2020 1:49 AM, "曹子 wrote:

HI folks:

     if from the call pass of z_swap, which with parameter,  

      do_swap(key.key, lock, 1);

    because is_spinlock is 1, so the lock would be released before invoke the actual switch function "arch_switch", 

which means there are nothing procteced the readyqueue of the scheduler, during the moment, if other cpus access the readyqueue, there would be a chance that

"_current" task be selected by other cpus before the register  context do the actual backup. so did this a bug?

 40 static ALWAYS_INLINE unsigned int do_swap(unsigned int key,

 41                                         ¦ struct k_spinlock *lock,

 42                                         ¦ int is_spinlock)

 43 {                   

 44         ARG_UNUSED(lock);

 45         struct k_thread *new_thread, *old_thread;

 46                     

 47 #ifdef CONFIG_EXECUTION_BENCHMARKING

 48         extern void read_timer_start_of_swap(void);

 49         read_timer_start_of_swap();

 50 #endif              

 51                     

 52         old_thread = _current;

 53                     

 54         z_check_stack_sentinel();

 55                     

 56         if (is_spinlock) {

 57                 k_spin_release(lock);

 58         }           

 59                     

 60         new_thread = z_get_next_ready_thread();

 61                     

 62         if (new_thread != old_thread) {

 63                 sys_trace_thread_switched_out();

 64 #ifdef CONFIG_TIMESLICING

 65                 z_reset_time_slice();

 66 #endif              

 67                     

 68                 old_thread->swap_retval = -EAGAIN;

 69                     

 70 #ifdef CONFIG_SMP   

 71                 _current_cpu->swap_ok = 0;

 72                     

 73                 new_thread->base.cpu = arch_curr_cpu()->id;

 74                     

 75                 if (!is_spinlock) {

 76                         z_smp_release_global_lock(new_thread);

 77                 }   

 78 #endif              

 79                 _current = new_thread;

 80                 arch_switch(new_thread->switch_handle,

 81                         ¦   ¦&old_thread->switch_handle); 84         }          

 85         

 83                 sys_trace_thread_switched_in();

 84         }          

 85         

 86         if (is_spinlock) {

 87                 arch_irq_unlock(key);

 88         } else {   

 89                 irq_unlock(key);

 90         }

 91                    

 92         return _current->swap_retval;

 93 }

 94       

曹子

珠海全志科技股份有限公司      BU1-PSW

地址:广东省珠海市高新区唐家湾镇科技2路9号

TEL:13824125580

Email:caozilong@...

网址: http://www.allwinnertech.com

 

 

 


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