Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754366Ab3GXOey (ORCPT ); Wed, 24 Jul 2013 10:34:54 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:45705 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751638Ab3GXOG3 (ORCPT ); Wed, 24 Jul 2013 10:06:29 -0400 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, "Greg Kroah-Hartman" , "Jiang Liu" , "Jiang Liu" Date: Wed, 24 Jul 2013 15:02:45 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [09/85] zram: use zram->lock to protect zram_free_page() in swap free notify path In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.101 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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2231 Lines: 61 3.2.49-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Jiang Liu commit 57ab048532c0d975538cebd4456491b5c34248f4 upstream. zram_slot_free_notify() is free-running without any protection from concurrent operations. So there are race conditions between zram_bvec_read()/zram_bvec_write() and zram_slot_free_notify(), and possible consequences include: 1) Trigger BUG_ON(!handle) on zram_bvec_write() side. 2) Access to freed pages on zram_bvec_read() side. 3) Break some fields (bad_compress, good_compress, pages_stored) in zram->stats if the swap layer makes concurrently call to zram_slot_free_notify(). So enhance zram_slot_free_notify() to acquire writer lock on zram->lock before calling zram_free_page(). Signed-off-by: Jiang Liu Signed-off-by: Greg Kroah-Hartman Signed-off-by: Ben Hutchings --- drivers/staging/zram/zram_drv.c | 2 ++ drivers/staging/zram/zram_drv.h | 5 +++-- 2 files changed, 5 insertions(+), 2 deletions(-) --- a/drivers/staging/zram/zram_drv.c +++ b/drivers/staging/zram/zram_drv.c @@ -702,7 +702,9 @@ static void zram_slot_free_notify(struct struct zram *zram; zram = bdev->bd_disk->private_data; + down_write(&zram->lock); zram_free_page(zram, index); + up_write(&zram->lock); zram_stat64_inc(zram, &zram->stats.notify_free); } --- a/drivers/staging/zram/zram_drv.h +++ b/drivers/staging/zram/zram_drv.h @@ -107,8 +107,9 @@ struct zram { void *compress_buffer; struct table *table; spinlock_t stat64_lock; /* protect 64-bit stats */ - struct rw_semaphore lock; /* protect compression buffers and table - * against concurrent read and writes */ + struct rw_semaphore lock; /* protect compression buffers, table, + * 32bit stat counters against concurrent + * notifications, reads and writes */ struct request_queue *queue; struct gendisk *disk; int init_done; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/