Messages in this thread | | | Date | Fri, 4 Jun 2010 10:59:18 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [linux-pm] Is it supposed to be ok to call del_gendisk while userspace is frozen? |
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On Fri, 4 Jun 2010, Maxim Levitsky wrote:
> On Thu, 2010-03-04 at 14:53 +0100, Pavel Machek wrote: > > Hi! > > > > > > journalling assumptions broken: commit block is there, but previous > > > > blocks are not intact. Data loss. > > > > > > > > ...and that was the first I could think about. Lets not do > > > > this. Barriers were invented for a reason. > > > > > > Very well. Then we still need a solution to the original problem: > > > Devices sometimes need to be unregistered during resume, but > > > del_gendisk() blocks on the writeback thread, which is frozen until > > > after the resume finishes. How do you suggest this be fixed? > > > > Avoid unregistering device during resume. Instead, return errors until > > resume is done and you can call del_gendisk? > > This won't help ether. The same driver needs to unregister perfectly > working device on suspend, because the user might replace the card > during suspend and fool the os. > There is a setting, CONFIG_MMC_UNSAFE_RESUME and I use it, but it isn't > default.
People have generally agreed that the best answer is to have del_gendisk always thaw the writeback thread.
> Anyway to revive that old thread, how about introducing new > del_gendisk_no_sync? > > A less safe version of del_gendisk, but which won't sync the filesystem. > Since driver knows that card is gone, there is no point of syncing it. > > (the sync is done by invalidate_partition, so some flag should be > propagated to it).
That might work for mmc, but it wouldn't help other drivers subject to the same problem.
Besides, it's subject to races. What if the card _isn't_ gone, but for some other reason the driver wants to unregister the device at a time when the writeback thread is frozen?
Alan Stern
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