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The following test case triggers BUG() in munlock_vma_pages_range():
int main(int argc, char *argv[])
{
int fd;
system("mount -t tmpfs -o huge=always none /mnt");
fd = open("/mnt/test", O_CREAT | O_RDWR);
ftruncate(fd, 4UL << 20);
mmap(NULL, 4UL << 20, PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_FIXED | MAP_LOCKED, fd, 0);
mmap(NULL, 4096, PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_LOCKED, fd, 0);
munlockall();
return 0;
}
The second mmap() create PTE-mapping of the first huge page in file. It
makes kernel munlock the page as we never keep PTE-mapped page mlocked.
On munlockall() when we handle vma created by the first mmap(),
munlock_vma_page() returns page_mask == 0, as the page is not mlocked
anymore. On next iteration follow_page_mask() return tail page, but
page_mask is HPAGE_NR_PAGES - 1. It makes us skip to the first tail
page of the next huge page and step on
VM_BUG_ON_PAGE(PageMlocked(page)).
The fix is not use the page_mask from follow_page_mask() at all. It has
no use for us.
Link: http://lkml.kernel.org/r/20170302150252.34120-1-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org> [4.5+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.