From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F2D46C282DD for ; Wed, 8 Jan 2020 19:49:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D03EE2070E for ; Wed, 8 Jan 2020 19:49:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728778AbgAHTtP (ORCPT ); Wed, 8 Jan 2020 14:49:15 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:43578 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730434AbgAHTqD (ORCPT ); Wed, 8 Jan 2020 14:46:03 -0500 Received: from [192.168.4.242] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1ipHHD-0006oh-6u; Wed, 08 Jan 2020 19:45:59 +0000 Received: from ben by deadeye with local (Exim 4.93) (envelope-from ) id 1ipHHC-007dmm-5X; Wed, 08 Jan 2020 19:45:58 +0000 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, Denis Kirjanov , "Android Kernel Team" , "Laura Abbott" , "Osvaldo Banuelos" , "John Stultz" , "Syed Rameez Mustafa" , "Arnd Bergmann" , "Subbaraman Narayanamurthy" , "Greg KH" , "Matt Wagantall" Date: Wed, 08 Jan 2020 19:43:27 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) X-Patchwork-Hint: ignore Subject: [PATCH 3.16 29/63] staging: ashmem: Avoid deadlock with mmap/shrink In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.242 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.81-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Laura Abbott commit 18e77054de741ef3ed2a2489bc9bf82a318b2d5e upstream. Both ashmem_mmap and ashmem_shrink take the ashmem_lock. It may be possible for ashmem_mmap to invoke ashmem_shrink: -000|mutex_lock(lock = 0x0) -001|ashmem_shrink(?, sc = 0x0) <--- try to take ashmem_mutex again -002|shrink_slab(shrink = 0xDA5F1CC0, nr_pages_scanned = 0, lru_pages -002|= -002|124) -003|try_to_free_pages(zonelist = 0x0, ?, ?, ?) -004|__alloc_pages_nodemask(gfp_mask = 21200, order = 1, zonelist = -004|0xC11D0940, -005|new_slab(s = 0xE4841E80, ?, node = -1) -006|__slab_alloc.isra.43.constprop.50(s = 0xE4841E80, gfpflags = -006|2148925462, ad -007|kmem_cache_alloc(s = 0xE4841E80, gfpflags = 208) -008|shmem_alloc_inode(?) -009|alloc_inode(sb = 0xE480E800) -010|new_inode_pseudo(?) -011|new_inode(?) -012|shmem_get_inode(sb = 0xE480E800, dir = 0x0, ?, dev = 0, flags = -012|187) -013|shmem_file_setup(?, ?, flags = 187) -014|ashmem_mmap(?, vma = 0xC5D64210) <---- Acquire ashmem_mutex -015|mmap_region(file = 0xDF8E2C00, addr = 1772974080, len = 233472, -015|flags = 57, -016|sys_mmap_pgoff(addr = 0, len = 230400, prot = 3, flags = 1, fd = -016|157, pgoff -017|ret_fast_syscall(asm) -->|exception -018|NUR:0x40097508(asm) ---|end of frame Avoid this deadlock by using mutex_trylock in ashmem_shrink; if the mutex is already held, do not attempt to shrink. Cc: Greg KH Cc: Android Kernel Team Reported-by: Matt Wagantall Reported-by: Syed Rameez Mustafa Reported-by: Osvaldo Banuelos Reported-by: Subbaraman Narayanamurthy Signed-off-by: Laura Abbott [jstultz: Minor commit message tweaks] Signed-off-by: John Stultz Signed-off-by: Greg Kroah-Hartman Cc: Arnd Bergmann Signed-off-by: Ben Hutchings --- drivers/staging/android/ashmem.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/drivers/staging/android/ashmem.c +++ b/drivers/staging/android/ashmem.c @@ -434,7 +434,9 @@ ashmem_shrink_scan(struct shrinker *shri if (!(sc->gfp_mask & __GFP_FS)) return SHRINK_STOP; - mutex_lock(&ashmem_mutex); + if (!mutex_trylock(&ashmem_mutex)) + return -1; + list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) { loff_t start = range->pgstart * PAGE_SIZE; loff_t end = (range->pgend + 1) * PAGE_SIZE;