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bf2f34a506
Now {pmd,pte}_mkdirty() set _PAGE_DIRTY bit unconditionally, this causes
random segmentation fault after commit 0ccf7f168e ("mm/thp: carry
over dirty bit when thp splits on pmd").
The reason is: when fork(), parent process use pmd_wrprotect() to clear
huge page's _PAGE_WRITE and _PAGE_DIRTY (for COW); then pte_mkdirty() set
_PAGE_DIRTY as well as _PAGE_MODIFIED while splitting dirty huge pages;
once _PAGE_DIRTY is set, there will be no tlb modify exception so the COW
machanism fails; and at last memory corruption occurred between parent
and child processes.
So, we should set _PAGE_DIRTY only when _PAGE_WRITE is set in {pmd,pte}_
mkdirty().
Cc: stable@vger.kernel.org
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
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.