Messages in this thread |  | | Date | Tue, 20 Feb 2007 11:08:54 -0500 | From | Chris Mason <> | Subject | Re: [PATCH] aio: propogate post-EIOCBQUEUED errors to completion event |
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On Tue, Feb 20, 2007 at 11:01:50AM -0500, Trond Myklebust wrote: > On Mon, 2007-02-19 at 19:21 -0500, Benjamin LaHaise wrote: > > On Mon, Feb 19, 2007 at 04:50:48PM -0500, Chris Mason wrote: > > > aio is not responsible for this particular synchronization. Those fixes > > > (if we make them) should come from other places. The patch is important > > > to get aio error handling right. > > > > > > I would argue that one common cause of the EIO is userland > > > error (mmap concurrent with O_DIRECT), and EIO is the correct answer. > > > > I disagree. That means that using the pagecache to synchronize things like > > the proposed online defragmentation will occasionally make O_DIRECT users > > fail. O_DIRECT doesn't prevent the sysadmin from copying files or other > > page cache uses, which implies that generating an error in these cases is > > horrifically broken. If only root could do it, I wouldn't complain, but > > this would seem to imply that user vs root holes still exist. > > We don't try to resolve "conflicting" writes between ordinary mmap() and > write(), so why should we be doing it for mmap and O_DIRECT? > > mmap() is designed to violate the ordinary mutex locks for write(), so > if a conflict arises, whether it be with O_DIRECT or ordinary writes > then it is a case of "last writer wins".
There are some strange O_DIRECT corner cases in here such that the 'last writer' may actually be a 'last reader' and winning can mean have a copy of the page in page cache older than the copy on disk.
One option is to have invalidate_inode_pages2_range continue if it can't toss a page but still return something that O_DIRECT ignores (living with the race), but it looks like I can make a launder_page op that does the right thing. I'll give it a shot.
-chris
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