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Date: Thu, 4 Mar 2010 01:23:13 +0100 From: "Rafael J. Wysocki" <rjw@...k.pl> To: Alan Stern <stern@...land.harvard.edu> Cc: Pavel Machek <pavel@....cz>, Jens Axboe <jens.axboe@...cle.com>, Maxim Levitsky <maximlevitsky@...il.com>, "linux-pm" <linux-pm@...ts.linux-foundation.org>, "linux-kernel" <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [linux-pm] Is it supposed to be ok to call del_gendisk while userspace is frozen? On Wednesday 03 March 2010, Alan Stern wrote: > On Wed, 3 Mar 2010, Pavel Machek wrote: > > > Hi! > > > > > > > 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? > > > > > > > > It is also there to avoid inconsistency between in-filesystem data and > > > > snapshot in hibernation image. > > > > > > A good point, although in this case I think it won't matter. Writing > > > out a dirty page twice (once right after taking the snapshot and then > > > again after resuming from hibernation) will leave the disk in a correct > > > state. > > > > No, I don't think so. Have you considered all the various journalling > > systems? > > > > Definitely not in presence of I/O errors. Commit block can only be > > written after previous blocks are successfully writen to the journal. > > > > So lets see: > > > > <snapshot> > > > > Write previous block, write commit block, write more blocks > > > > <hibernation powerdown, restart> > > > > Error writing previous block (block now contains garbage), leading to > > kernel panic > > > > <restart> > > > > 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? I thought about thawing the writeback thread earlier in such cases. Would that makes sense / is it doable at all? Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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