Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 31 Oct 2012 00:00:56 +0800 | Subject | Re: [PATCH v3 2/6] PM / Runtime: introduce pm_runtime_set[get]_memalloc_noio() | From | Ming Lei <> |
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On Tue, Oct 30, 2012 at 11:38 PM, Alan Stern <stern@rowland.harvard.edu> wrote:
> > Okay, I see your point. But acquiring the lock here doesn't solve the > problem. Suppose a thread is about to reset a USB mass-storage device. > It acquires the lock and sees that the noio flag is clear. But before > it can issue the reset, another thread sets the noio flag.
If the USB mass-storage device is being reseted, the flag should be set already generally. If the flag is still unset, that means the disk/network device isn't added into system(or removed just now), so memory allocation with block I/O should be allowed during the reset. Looks it isn't one problem, isn't it?
> I'm not sure what the best solution is. > >> The lock needn't to be held when the function is called inside >> pm_runtime_set_memalloc_noio(), so the bitfield flag should >> be checked directly without holding power lock in dev_memalloc_noio(). > > Yes. > > A couple of other things... Runtime resume can be blocked by runtime > suspend, if a resume is requested while the suspend is in progress. > Therefore the runtime suspend code also needs to save-set-restore the > noio flag.
Looks the simplest approach is to handle the noio flag thing at the start and end of rpm_resume.
> Also, we should set the noio flag at the start of > usb_stor_control_thread, because everything that thread does can > potentially block an I/O operation.
Yes, it should be done, and all GFP_NOIO in usbcore should be converted into GFP_KERNEL together. And the work shouldn't be started until the patchset is merged.
> Lastly, pm_runtime_get_memalloc_noio always returns false when > CONFIG_PM_RUNTIME is disabled. But we still need to prevent I/O during > usb_reset_device even when there's no runtime PM. Maybe the simplest > answer is always to set noio during resets. That would also help with > the race described above.
I have thought about this. IMO, pm_runtime_get_memalloc_noio should return true always if CONFIG_PM_RUNTIME is unset.
Thanks, -- Ming Lei
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