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Re: Kernels v4.9+ cause short reads of block devices

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On Wed, Aug 23, 2017 at 12:15 PM, Doug Nazar <nazard@nazar.ca> wrote:
> The following commits cause short reads of block devices, however writes are
> still allowed.
>
> c2a9737f45e2 ("vfs,mm: fix a dead loop in truncate_inode_pages_range()")
> d05c5f7ba164 ("vfs,mm: fix return value of read() at s_maxbytes")
>
> When e2fsck sees this, it thinks it's a bad sector and tries to write a
> block of nulls which overwrites the valid data.

Hmm. Block devices shouldn't have issues with s_maxbytes, and I'm
surprised that nobody has seen that before.

> Device is LVM over 2 x RAID-5 on an old 32bit desktop.
>
> RO    RA   SSZ   BSZ   StartSec            Size   Device
> rw  4096   512  4096          0   9748044840960 /dev/Storage/Main

.. and the problem may be as simple as just a missing initialization
of s_maxbytes for blockdev_superblock.

Does the attcahed trivial one-liner fix things for you?

Al, if it really is this simple, how come nobody even noticed?

Also, I do wonder if that check in do_generic_file_read() should just
unconditionally use MAX_LFS_FILESIZE, since the whole point there is
really about the index wrap-around, not about any underlying
filesystem limits per se.

And that's exactly what MAX_LFS_FILESIZE is - the maximum size that
fits in the page index.

              Linus

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Re: Kernels v4.9+ cause short reads of block devices Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-23 21:40 +0200
  Re: Kernels v4.9+ cause short reads of block devices Doug Nazar <nazard@nazar.ca> - 2017-08-23 22:00 +0200
    Re: Kernels v4.9+ cause short reads of block devices Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-23 22:20 +0200
      Re: Kernels v4.9+ cause short reads of block devices Andreas Dilger <adilger@dilger.ca> - 2017-08-23 23:10 +0200
        Re: Kernels v4.9+ cause short reads of block devices Doug Nazar <nazard@nazar.ca> - 2017-08-24 12:30 +0200
          Re: Kernels v4.9+ cause short reads of block devices Dave Kleikamp <dave.kleikamp@oracle.com> - 2017-08-24 17:30 +0200
      Re: Kernels v4.9+ cause short reads of block devices Doug Nazar <nazard@nazar.ca> - 2017-08-24 12:10 +0200

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