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> Cc: Hugh Dickins <hughd@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 @@ -1547,19 +1547,23 @@ 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 */ _
