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On s390 there currently is no implementation of pud_write(). That was ok as long as we had our own implementation of get_user_pages_fast() which checked for pud protection by testing the bit directly w/o using pud_write(). The other callers of pud_write() are not reachable on s390. After commit1a42010cdc("s390/mm: convert to the generic get_user_pages_fast code") we use the generic get_user_pages_fast(), which does call pud_write() in pud_access_permitted() for FOLL_WRITE access on a large pud. Without an s390 specific pud_write(), the generic version is called, which contains a BUG() statement to remind us that we don't have a proper implementation. This results in a kernel panic. Fix this by providing an implementation of pud_write(). Cc: <stable@vger.kernel.org> # 5.2+ Fixes:1a42010cdc("s390/mm: convert to the generic get_user_pages_fast code") Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com> Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.