On Sat, 2014-02-15 at 14:38 -0500, Peter Hurley wrote: > Since commit a2c1c57be8d9fd5b716113c8991d3d702eeacf77, > workqueue: consider work function when searching for busy work items > work items whose work functions are re-assigned are no longer guaranteed > non-reentrancy with the previously assigned work function. For example, > > PREPARE_WORK(&work, funcA) > schedule_work(&work) > . > < funcA starts > > . > PREPARE_WORK(&work, funcB) > schedule_work(&work) > > funcA() may run concurrently with funcB(). > > The work item non-reentrancy guarantee is a crucial design guarantee > which, if violated, may not have obvious consequences. For example, > the entire firewire subsystem expects the as-documented per-work item > non-reentrancy guarantee, which was the behavior prior to the above > commit, not the per-work function + per-work item behavior since. > > Document the known exceptions to this guarantee. [...] It never would have occurred to me that you could safely change the function for a work item that is already scheduled or running. Especially given that PREPARE_WORK() is just a simple assignment (i.e. no serialisation). Perhaps there is a need to document more generally how PREPARE_WORK() can be used, not just this quirk of reentrancy. Ben. -- Ben Hutchings Nothing is ever a complete failure; it can always serve as a bad example.
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