Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH, RFC] check for frozen filesystems in the mmap path | Date | Wed, 22 Apr 2009 13:49:21 +0900 (JST) |
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> > 2. this logic kill multi thread application. > > > > this logic mean mmap_sem grabbing until unfreeze. > > it mean othrer thread in the same process can't page-fault although > > it don't touch frozen-sb. > > it seems strange. > > Hm, I hadn't thought about this ... On the one hand, ->page_mkwrite can > already sleep, though a userspace freeze/unfreeze could potentially take > much much longer. freeze/unfreeze *should* happen very quickly, but > nothing enforces that. > > Do you have any suggestions?
One more comment.
I read ioctl_fsfreeze() and freeze_bdev(), it call __fsync_super(). Oh, I don't think __fsync_suepr is very quick.
So, page-fault have one unique characteristics. if page-fault return 0 without pte change, page-fault is occur again soon. then, if you need long time waiting, I think you can use following technique.
unlock mmap_sem wait long-time lock mmap_sem goto out;
it cause page-fault counter increment twice unintesionally. but no problem. fs-freeze is not freqently event.
Am I missing anything?
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