Re: [git pull] vfs and fs fixes

From: J. Bruce Fields
Date: Tue Apr 17 2012 - 13:06:12 EST

On Tue, Apr 17, 2012 at 09:33:06AM -0700, Linus Torvalds wrote:
> On Tue, Apr 17, 2012 at 9:22 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> >
> > Ugh, no, I think you're right:
> >
> > Â Â Â Ârename A/a->A/b
> > Â Â Â Ârename B/b->B/b
> >
> > where A/a and B/a are the same file, and A/b and B/b are the same file,
> > can result in the first rename holding the lock on A and a and waiting
> > on b, and the second holding the lock on B and b and waiting on a.
> In fact I don't think you need even that much. Just a simple
> touch a
> ln a b
> mv a b
> looks like it should deadlock on itself, no? source and dest inodes
> will be the same, so the mutex_lock() will just deadlock without even
> any ABBA race.
> (I didn't really check - maybe there is some reason that doesn't happen).

Yeah, rename has that funny exception that makes the above a no-op, so I
think that's safe.

But the patch is still wrong; back to the drawing board.

Maybe a paper bag over my head will help my concentration....

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