Commit 7f3bfab5 authored by Jann Horn's avatar Jann Horn Committed by Linus Torvalds
Browse files

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.

Signed-off-by: default avatarJann Horn <jannh@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Eric W . Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200827114932.3572699-7-jannh@google.com


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a07279c9

mm/gup.c

+10 −6
Original line number Diff line number Diff line
@@ -1547,19 +1547,23 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start, 
 * 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 */