On Sun, 23 Mar 2008, Rafael J. Wysocki wrote: > On Sunday, 23 of March 2008, Alan Stern wrote: > > On Sat, 22 Mar 2008, Rafael J. Wysocki wrote: > > > [--snip--] > > > > No, you have missed the entire point. The problem doesn't exist in the > > current code; it exists only if we switch over to using a single list. > > Routines like dpm_suspend() won't be able to use list_for_each_entry() > > to traverse the list because entries may be removed by other threads > > during the traversal. Even list_for_each_entry_safe() won't work > > correctly without careful attention to details. > > Ah, ok. Thanks for the clarification. > > Doesn't it help that we traverse the list under dpm_list_mtx? Anyone who > removes an entry is required to take dpm_list_mtx that we're holding while > the list is traversed except when the callbacks are invoked. It doesn't help. What _does_ help is the fact that these traversals are all serialized (since only one thread can carry out a system sleep at any time). > The only problem I see is when the device currently being handled is removed > from the list by a concurrent thread. Is that you were referring to? Yes, that is the problem. If you try to work around it by using list_for_each_entry_safe() then you run into a problem when a concurrent thread removes the device _following_ the one being handled (or when the device being handled is the last one on the list and a concurrent thread registers a new device, which can only happen in dpm_prepare()). It's not hard to fix. Just something to be aware of. Alan Stern P.S.: Oh yes, another related issue... We should call get_device() and put_device() while holding dpm_list_mtx. Otherwise the device structure might vanish when the callbacks are invoked. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
