Re: [PATCH 1/3] xfs: Do not unshare ranges beyond EOF

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Christoph Hellwig <hch@xxxxxxxxxxxxx> 于2024年9月20日周五 22:23写道:
>
> On Fri, Sep 20, 2024 at 08:26:21PM +0800, Julian Sun wrote:
> > Attempting to unshare extents beyond EOF will trigger
> > the need zeroing case, which in turn triggers a warning.
> > Therefore, let's skip the unshare process if extents are
> > beyond EOF.
> >
> > Reported-and-tested-by: syzbot+296b1c84b9cbf306e5a0@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Closes: https://syzkaller.appspot.com/bug?extid=296b1c84b9cbf306e5a0
> > Fixes: 32a38a499104 ("iomap: use write_begin to read pages to unshare")
> > Inspired-by: Dave Chinner <david@xxxxxxxxxxxxx>
> > Signed-off-by: Julian Sun <sunjunchao2870@xxxxxxxxx>
> > ---
> >  fs/xfs/xfs_reflink.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> > index 6fde6ec8092f..65509ff6aba0 100644
> > --- a/fs/xfs/xfs_reflink.c
> > +++ b/fs/xfs/xfs_reflink.c
> > @@ -3,6 +3,7 @@
> >   * Copyright (C) 2016 Oracle.  All Rights Reserved.
> >   * Author: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >   */
> > +#include "linux/fs.h"
>
> This really should not be needed (and is the wrong way to include
> non-local headers anyway).

Yes, it was added automatically by vscode... I will recheck the patch
before sending it.
>
> >  #include "xfs.h"
> >  #include "xfs_fs.h"
> >  #include "xfs_shared.h"
> > @@ -1669,6 +1670,9 @@ xfs_reflink_unshare(
> >
> >       if (!xfs_is_reflink_inode(ip))
> >               return 0;
> > +     /* don't try to unshare any ranges beyond EOF. */
> > +     if (offset + len > i_size_read(inode))
> > +             len = i_size_read(inode) - offset;
>
> So i_size is a byte granularity value, but later on iomap_file_unshare
> operates on blocks.  If you reduce the value like this here this means
> we can't ever unshare the last block of a file if the file size is
> not block aligned, which feels odd.

Got it, will fix it in patch v2. Thanks for your review and explantion.
>

Thanks,
-- 
Julian Sun <sunjunchao2870@xxxxxxxxx>





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