Re: [PATCH 2/9] vfs: export do_splice_direct() to modules

From: Al Viro
Date: Tue Mar 19 2013 - 17:38:43 EST

On Tue, Mar 19, 2013 at 09:25:43PM +0100, Jan Kara wrote:
> > BTW, having sb_start_write() buried in individual ->splice_write() is
> > asking for trouble; could you describe the rules for that? E.g. where
> > does it nest wrt filesystem-private locks? XFS iolock, for example...
> Generally, the freeze protection should be the outermost lock taken (so
> that we mitigate possibility of blocking readers when waiting for fs to
> unfreeze). So it ranks above i_mutex, or XFS' ilock and iolock.

Welcome to deadlock, then:
xfs_ilock(ip, XFS_IOLOCK_EXCL);
ret = generic_file_splice_write(pipe, outfilp, ppos, count, flags);

> It seems that I screwed this up for ->splice_write() :-| If we are going to
> move out sb_start_write() out of filesystems' hands into do_splice_from()
> then we should likely do the same with ->aio_write(). Hmm?

Yes, I've a tentative patch doing just that; will push tonight.
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