On Tue, 23 Feb 2010, Jens Axboe wrote: > On Tue, Feb 16 2010, Alan Stern wrote: > > On Mon, 15 Feb 2010, Rafael J. Wysocki wrote: > > > > > On Monday 15 February 2010, Maxim Levitsky wrote: > > > > On Sat, 2010-02-13 at 15:29 +0200, Maxim Levitsky wrote: > > > > > I noticed that currently calling del_gendisk leads to sure deadlock if > > > > > attemped from .suspend or .resume functions. > > > > > > Well, it shouldn't be called from there, then. > > > > Even if drivers avoid calling it from within suspend methods, they have > > to be able to call it from within resume methods. After all, the > > resume method may find that the disk's device has vanished. > > del_gendisk() needs process context at least, since it'll sleep (not > just for sync/invalidate, but other parts of the destruction as well). That's not a problem; suspend and resume run in process context. > > This is a matter for Jens. Is the bdi writeback task freezable? If it > > is, should it be made unfreezable? > > I'm not a big expect on what tasks should be freezable or not. As it > stands, the writeback tasks will attempt to freeze and thaw with the > system. I guess that screws the sync from resume call, since it's not > running and the sync will wait for it to retrieve and finish that work > item. > > To the suspend experts - can we safely mark the writeback tasks as > non-freezable? The reason for freezing those tasks is to avoid writebacks at random times during a system sleep transition, when the underlying device may already be suspended, right? In principle, a device's writeback task could be unfrozen immediately after the device is resumed. In practice this might not solve the problem, since the del_gendisk() call occurs _within_ the device's resume routine. I suppose del_gendisk() could be made responsible for unfreezing the writeback task. The best solution would be to have del_gendisk() avoid waiting for the writeback task in cases where the underlying device has been removed. I don't know if that is feasible, however. Alan Stern P.S.: Jens, given a pointer to a struct gendisk or to a struct request_queue, is there a good way to tell whether there any dirty buffers for that device waiting to be written out? This is for purposes of runtime power management -- in the initial implementation, I want to avoid powering-down a block device if it is open or has any dirty buffers. In other words, only completely idle devices should be powered down (a good example would be a card reader with no memory card inserted). _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
