Messages in this thread | | | Date | Thu, 05 Jul 2012 13:31:43 +0800 | From | Michael Wang <> | Subject | [RFC BUG] There is a potential bug in "yield_to" |
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Hi, All
I found there may be a potential bug in "yield_to":
local_irq_save(flags); rq = this_rq();
again:
//task's rq may already changed in "sched_move_task"
p_rq = task_rq(p); double_rq_lock(rq, p_rq); while (task_rq(p) != p_rq) { double_rq_unlock(rq, p_rq); goto again; }
I think it may happen in this scene:
cpu 0 cpu 1(task a)
yield_to { disable_irq sched_move_task { rq = this_rq(); task_rq_lock(task a) double_rq_lock
hold lock of rq 1 set_task_rq //task rq changed release lock of rq 1
hold lock of rq 1 but task b no longer there
set rq 1's current to skip which is not task a
which means we hold a rq's lock but it's current is not the one should do yield.
Only "sched_move_task" will cause this issue as it will move the task which is still running.
The bug will make the task who want to do yield failed to set skip buddy to himself, but to a innocent task instead, not very harmful and almost impossible to occur in normal, but should we fix it with another check "rq == this_rq()"?
Regards, Michael Wang
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