On Wed, 31 Oct 2012, Ming Lei wrote: > On Tue, Oct 30, 2012 at 11:38 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> 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? As Oliver said, it can be a problem. > > 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. That's okay as long as the only user of pm_runtime_get_memalloc_noio (apart from the runtime PM core) is usbcore. Alan Stern -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>