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Re: [bug] pwritev02 hang on s390x with 4.8.0-rc7

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On Tue, Sep 20, 2016 at 01:11:41PM -0400, Jan Stancek wrote:

> I ran all syscalls tests from LTP, and I see a change in behaviour
> of couple other tests (writev01, writev03 and writev04 [1]) in 4.8.0-rc7.
> 
> These call writev() with partially invalid iovecs, and now fail with
> EFAULT, while with previous -rc6 kernel they returned number of bytes
> written before they encountered invalid iovec record.
> This should be reproducible also on x86.

Known, discussed and considered legitimate.  It's not so much EFAULT vs short
write, it's how far do we shorten the write.  Change consists of removing
an accidental (and undocumented) property of iovec boundaries wrt write
shortening.  Usually an invalid address anywhere in the data we are asked to
write leads to write shortened to the last pagecache boundary (i.e file
position multiple of page size) entirely covered by valid data.  It is
filesystem-dependent and already deep in nasal demon territory.  writev,
pretty much by accident, never shortened past an iovec boundary.  That's
what got changed - now the rules are same as they are for all writes.

Having an LTP test (as opposed to actual real-world code) deliberately
stepping into that and checking how far does the shortening go means just
one thing: update the test.

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[bug] pwritev02 hang on s390x with 4.8.0-rc7 Jan Stancek <jstancek@redhat.com> - 2016-09-20 15:00 +0200
  Re: [bug] pwritev02 hang on s390x with 4.8.0-rc7 Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-20 17:10 +0200
    Re: [bug] pwritev02 hang on s390x with 4.8.0-rc7 Jan Stancek <jstancek@redhat.com> - 2016-09-20 19:20 +0200
      Re: [bug] pwritev02 hang on s390x with 4.8.0-rc7 Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-20 19:40 +0200
      [PATCH] fix fault_in_multipages_...() on architectures with no-op  access_ok() Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-20 21:10 +0200
        Re: [PATCH] fix fault_in_multipages_...() on architectures with no-op access_ok() Linus Torvalds <torvalds@linux-foundation.org> - 2016-09-20 22:30 +0200
          Re: [PATCH] fix fault_in_multipages_...() on architectures with  no-op access_ok() Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-20 22:40 +0200
            Re: [PATCH] fix fault_in_multipages_...() on architectures with no-op access_ok() Linus Torvalds <torvalds@linux-foundation.org> - 2016-09-20 22:50 +0200
              Re: [PATCH] fix fault_in_multipages_...() on architectures with  no-op access_ok() Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-20 23:10 +0200
                Re: [PATCH] fix fault_in_multipages_...() on architectures with  no-op access_ok() Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-20 23:40 +0200
                Re: [PATCH] fix fault_in_multipages_...() on architectures with no-op access_ok() Linus Torvalds <torvalds@linux-foundation.org> - 2016-09-21 01:50 +0200
                Re: [PATCH] fix fault_in_multipages_...() on architectures with  no-op access_ok() Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-21 02:40 +0200

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