The patch titled Subject: mm, thp: fix incorrect unmap behavior for private pages has been added to the -mm tree. Its filename is mm-thp-fix-incorrect-unmap-behavior-for-private-pages.patch

This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mm-thp-fix-incorrect-unmap-behavio... and later at https://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-fix-incorrect-unmap-behavio...

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------------------------------------------------------ From: Rongwei Wang rongwei.wang@linux.alibaba.com Subject: mm, thp: fix incorrect unmap behavior for private pages

When truncating pagecache on file THP, the private pages of a process should not be unmapped mapping. This incorrect behavior on a dynamic shared libraries which will cause related processes to happen core dump.

A simple test for a DSO (Prerequisite is the DSO mapped in file THP):

int main(int argc, char *argv[]) { int fd;

fd = open(argv[1], O_WRONLY); if (fd < 0) { perror("open"); }

close(fd); return 0; }

The test only to open a target DSO, and do nothing. But this operation will lead one or more process to happen core dump. This patch mainly to fix this bug.

Link: https://lkml.kernel.org/r/20211025092134.18562-3-rongwei.wang@linux.alibaba.... Fixes: eb6ecbed0aa2 ("mm, thp: relax the VM_DENYWRITE constraint on file-backed THPs") Signed-off-by: Rongwei Wang rongwei.wang@linux.alibaba.com Tested-by: Xu Yu xuyu@linux.alibaba.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Song Liu song@kernel.org Cc: William Kucharski william.kucharski@oracle.com Cc: Hugh Dickins hughd@google.com Cc: Yang Shi shy828301@gmail.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Collin Fijalkovich cfijalkovich@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/open.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/fs/open.c~mm-thp-fix-incorrect-unmap-behavior-for-private-pages +++ a/fs/open.c @@ -857,8 +857,17 @@ static int do_dentry_open(struct file *f */ smp_mb(); if (filemap_nr_thps(inode->i_mapping)) { + struct address_space *mapping = inode->i_mapping; + filemap_invalidate_lock(inode->i_mapping); - truncate_pagecache(inode, 0); + /* + * unmap_mapping_range just need to be called once + * here, because the private pages is not need to be + * unmapped mapping (e.g. data segment of dynamic + * shared libraries here). + */ + unmap_mapping_range(mapping, 0, 0, 0); + truncate_inode_pages(mapping, 0); filemap_invalidate_unlock(inode->i_mapping); } } _

Patches currently in -mm which might be from rongwei.wang@linux.alibaba.com are

mm-thp-bail-out-early-in-collapse_file-for-writeback-page.patch mm-thp-lock-filemap-when-truncating-page-cache.patch mm-thp-fix-incorrect-unmap-behavior-for-private-pages.patch mm-damon-dbgfs-remove-unnecessary-variables.patch