Re: [PATCH 2/9] vfs: export do_splice_direct() to modules
From: Dave Chinner
Date: Sun Mar 17 2013 - 22:32:25 EST
On Sun, Mar 17, 2013 at 01:06:59PM +0000, David Howells wrote:
> Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> > Export do_splice_direct() to modules. Needed by overlay filesystem.
> Apparently you cannot call this from any function that is holding an i_mutex
> if the target of the splice uses generic_file_splice_write().
> The problem is a potential deadlock situation:
> We have places already that do:
> This can be found in do_last() for example.
> However, mnt_want_write() calls sb_start_write() as does
> generic_file_splice_write(). So now in ovl_copy_up_locked() you're adding:
> which lockdep reports as a potential ABBA deadlock.
> Now, looking at __sb_start_write(), I'm not entirely sure how the deadlock
> might operate, so it's possible that this is a false alarm. Maybe Jan Kara can
> illuminate further, so I've added him to the cc list.
> I've attached the report I got with unionmount.
There's plenty of problems with splice locking that can lead to
deadlocks. Here's another that's been known for ages:
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/