linux-kernel - Re: iov_iter

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Message-ID: <20170910200547.GD5426@ZenIV.linux.org.uk>
Date:   Sun, 10 Sep 2017 21:05:48 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Dave Jones <davej@...emonkey.org.uk>,
        Dave Chinner <david@...morbit.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        linux-xfs@...r.kernel.org
Subject: Re: iov_iter_pipe warning.

On Sun, Sep 10, 2017 at 12:07:10PM -0400, Dave Jones wrote:
> On Sun, Sep 10, 2017 at 03:57:21AM +0100, Al Viro wrote:
>  > On Sat, Sep 09, 2017 at 09:07:56PM -0400, Dave Jones wrote:
>  > 
>  > > With this in place, I'm still seeing -EBUSY from invalidate_inode_pages2_range
>  > > which doesn't end well...
>  > 
>  > Different issue, and I'm not sure why that WARN_ON() is there in the
>  > first place.  Note that in a similar situation generic_file_direct_write()
>  > simply buggers off and lets the caller do buffered write...
>  > 
>  > iov_iter_pipe() warning is a sign of ->read_iter() on pipe-backed iov_iter
>  > putting into the pipe more than it claims to have done.
> 
> (from a rerun after hitting that EBUSY warn; hence the taint)
> 
> WARNING: CPU: 0 PID: 14154 at fs/iomap.c:1055 iomap_dio_rw+0x78e/0x840

... and that's another invalidate_inode_pages2_range() in the same
sucker.  Again, compare with generic_file_direct_write()...

I don't believe that this one has anything splice-specific to do with it.
And its only relation to iov_iter_pipe() splat is that it's in the same
fs/iomap.c...