linux-kernel - Re: [PATCH] xfs: fix BUG_ON in xfs

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Date:   Mon, 27 Mar 2023 19:03:41 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "yebin (H)" <yebin10@...wei.com>, Ye Bin <yebin@...weicloud.com>,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xfs: fix BUG_ON in xfs_getbmap()

On Mon, Mar 27, 2023 at 06:47:54PM -0700, Christoph Hellwig wrote:
> On Mon, Mar 27, 2023 at 06:43:28PM -0700, Darrick J. Wong wrote:
> > <shrug> Seeing as the data fork mappings can change the instant the
> > ILOCK drops, I'm not /that/ worried about users seeing a delalloc
> > mapping even if the user requested a flush.  The results are already
> > obsolete when they get to userspace, unless the application software has
> > found another means to lock out access to the file.
> 
> That is true, but then again the users asked to not see delalloc
> mappings, so we really shouldn't report one, right?

Yeah, I suppose so.  I wonder how many programs there are out there that
don't pass in BMV_IF_DELALLOC /and/ can't handle that?  But I suppose
taking MMAP_EXCL is good enough to shut up the obvious assertion vector.

The COW implementation probably ought to be doing the flush too.

--D