From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jann Horn Date: Wed, 29 Apr 2020 21:49:54 +0000 Subject: [PATCH v2 5/5] mm/gup: Take mmap_sem in get_dump_page() Message-Id: <20200429214954.44866-6-jannh@google.com> List-Id: References: <20200429214954.44866-1-jannh@google.com> In-Reply-To: <20200429214954.44866-1-jannh@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Andrew Morton Cc: Rich Felker , linux-c6x-dev@linux-c6x.org, Yoshinori Sato , linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org, Oleg Nesterov , linux-mm@kvack.org, Alexander Viro , Mark Salter , linux-fsdevel@vger.kernel.org, Russell King , Aurelien Jacquiot , Linus Torvalds , Christoph Hellwig , linux-arm-kernel@lists.infradead.org, "Eric W . Biederman" Properly take the mmap_sem before calling into the GUP code from get_dump_page(); and play nice, allowing the GUP code to drop the mmap_sem 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: Jann Horn --- mm/gup.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 9a7e83772f1fe..03f659ddd830a 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1548,19 +1548,23 @@ static long __get_user_pages_locked(struct task_struct *tsk, * 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_sem, but after all other threads have been killed. + * Called without mmap_sem (takes and releases the mmap_sem by itself). */ 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(current, current->mm, addr, 1, - FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma, - NULL) < 1) + if (down_read_killable(&mm->mmap_sem)) return NULL; - flush_cache_page(vma, addr, page_to_pfn(page)); - return page; + ret = __get_user_pages_locked(current, mm, addr, 1, &page, NULL, + &locked, + FOLL_FORCE | FOLL_DUMP | FOLL_GET); + if (locked) + up_read(&mm->mmap_sem); + return (ret = 1) ? page : NULL; } #if defined(CONFIG_FS_DAX) || defined (CONFIG_CMA) -- 2.26.2.526.g744177e7f7-goog