The patch titled
Subject: mm/gup: take mmap_lock in get_dump_page()
has been added to the -mm tree. Its filename is
mm-gup-take-mmap_lock-in-get_dump_page.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-gup-take-mmap_lock-in-get_dump_page.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-gup-take-mmap_lock-in-get_dump_page.patch
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------------------------------------------------------
From: Jann Horn <jannh@xxxxxxxxxx>
Subject: mm/gup: take mmap_lock in get_dump_page()
Properly take the mmap_lock before calling into the GUP code from
get_dump_page(); and play nice, allowing the GUP code to drop the
mmap_lock if it has to sleep.
As Linus pointed out, we don't actually need the VMA because
__get_user_pages() will flush the dcache for us if necessary.
Link: http://lkml.kernel.org/r/20200827114932.3572699-7-jannh@xxxxxxxxxx
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Acked-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: "Eric W . Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/gup.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
--- a/mm/gup.c~mm-gup-take-mmap_lock-in-get_dump_page
+++ a/mm/gup.c
@@ -1552,19 +1552,23 @@ finish_or_fault:
* NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
* allowing a hole to be left in the corefile to save diskspace.
*
- * Called without mmap_lock, but after all other threads have been killed.
+ * Called without mmap_lock (takes and releases the mmap_lock by itself).
*/
#ifdef CONFIG_ELF_CORE
struct page *get_dump_page(unsigned long addr)
{
- struct vm_area_struct *vma;
+ struct mm_struct *mm = current->mm;
struct page *page;
+ int locked = 1;
+ int ret;
- if (__get_user_pages_locked(current->mm, addr, 1, &page, &vma, NULL,
- FOLL_FORCE | FOLL_DUMP | FOLL_GET) < 1)
+ if (mmap_read_lock_killable(mm))
return NULL;
- flush_cache_page(vma, addr, page_to_pfn(page));
- return page;
+ ret = __get_user_pages_locked(mm, addr, 1, &page, NULL, &locked,
+ FOLL_FORCE | FOLL_DUMP | FOLL_GET);
+ if (locked)
+ mmap_read_unlock(mm);
+ return (ret == 1) ? page : NULL;
}
#endif /* CONFIG_ELF_CORE */
_
Patches currently in -mm which might be from jannh@xxxxxxxxxx are
binfmt_elf_fdpic-stop-using-dump_emit-on-user-pointers-on-mmu.patch
coredump-let-dump_emit-bail-out-on-short-writes.patch
coredump-refactor-page-range-dumping-into-common-helper.patch
coredump-rework-elf-elf_fdpic-vma_dump_size-into-common-helper.patch
binfmt_elf-binfmt_elf_fdpic-use-a-vma-list-snapshot.patch
mm-gup-take-mmap_lock-in-get_dump_page.patch
mm-remove-the-now-unnecessary-mmget_still_valid-hack.patch
