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workqueue: allow work_on_cpu() to be called recursively
If the @fn call work_on_cpu() again, the lockdep will complain: > [ INFO: possible recursive locking detected ] > 3.11.0-rc1-lockdep-fix-a #6 Not tainted > --------------------------------------------- > kworker/0:1/142 is trying to acquire lock: > ((&wfc.work)){+.+.+.}, at: [<ffffffff81077100>] flush_work+0x0/0xb0 > > but task is already holding lock: > ((&wfc.work)){+.+.+.}, at: [<ffffffff81075dd9>] process_one_work+0x169/0x610 > > other info that might help us debug this: > Possible unsafe locking scenario: > > CPU0 > ---- > lock((&wfc.work)); > lock((&wfc.work)); > > *** DEADLOCK *** It is false-positive lockdep report. In this sutiation, the two "wfc"s of the two work_on_cpu() are different, they are both on stack. flush_work() can't be deadlock. To fix this, we need to avoid the lockdep checking in this case, thus we instroduce a internal __flush_work() which skip the lockdep. tj: Minor comment adjustment. Signed-off-by: Lai Jiangshan <[email protected]> Reported-by: "Srivatsa S. Bhat" <[email protected]> Reported-by: Alexander Duyck <[email protected]> Signed-off-by: Tejun Heo <[email protected]>
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