Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752203AbbEKWZR (ORCPT ); Mon, 11 May 2015 18:25:17 -0400 Received: from mail-pa0-f50.google.com ([209.85.220.50]:35260 "EHLO mail-pa0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751626AbbEKWZO (ORCPT ); Mon, 11 May 2015 18:25:14 -0400 Date: Mon, 11 May 2015 15:25:05 -0700 From: Brian Norris To: "Cantavenera, Giuseppe (EXT-Other - DE/Ulm)" Cc: "linux-mtd@lists.infradead.org" , "Restelli, Lorenzo (EXT-Other - DE/Ulm)" , "dwmw2@infradead.org" , "stable@vger.kernel.org" , "Sverdlin, Alexander (Nokia - DE/Ulm)" , zhangxingcai , "fengfuqiu@huawei.com" , "tanhaijun@huawei.com" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] mtd: fix: avoid race condition when accessing mtd->usecount Message-ID: <20150511222505.GI32500@ld-irv-0074> References: <1429611622-2652-1-git-send-email-giuseppe.cantavenera.ext@nokia.com> <20150508001012.GV32500@ld-irv-0074> <20150508001745.GW32500@ld-irv-0074> <20150508002649.GX32500@ld-irv-0074> <362FEC998FA6CC42BC5BA5B7BA75E0970D5A08FA@DEMUMBX009.nsn-intra.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <362FEC998FA6CC42BC5BA5B7BA75E0970D5A08FA@DEMUMBX009.nsn-intra.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2596 Lines: 70 On Mon, May 11, 2015 at 07:44:26AM +0000, Cantavenera, Giuseppe (EXT-Other - DE/Ulm) wrote: > > -----Original Message----- > > From: ext Brian Norris [mailto:computersforpeace@gmail.com] > > Sent: Friday, May 08, 2015 2:27 AM > > To: Cantavenera, Giuseppe (EXT-Other - DE/Ulm) > > Cc: linux-mtd@lists.infradead.org; Restelli, Lorenzo (EXT-Other - > > DE/Ulm); dwmw2@infradead.org; stable@vger.kernel.org; Sverdlin, > > Alexander (Nokia - DE/Ulm); zhangxingcai; fengfuqiu@huawei.com; > > tanhaijun@huawei.com; linux-kernel@vger.kernel.org > > Subject: Re: [PATCH] mtd: fix: avoid race condition when accessing mtd- > > >usecount > > > > On Thu, May 07, 2015 at 05:17:45PM -0700, Brian Norris wrote: > > > On Thu, May 07, 2015 at 05:10:12PM -0700, Brian Norris wrote: > > > > On Tue, Apr 21, 2015 at 12:20:22PM +0200, Giuseppe Cantavenera > > wrote: > > > > > @@ -484,7 +486,7 @@ int del_mtd_blktrans_dev(struct > > mtd_blktrans_dev *old) > > > > > if (old->open) { > > > > > if (old->tr->release) > > > > > old->tr->release(old); > > > > > - __put_mtd_device(old->mtd); > > > > > + put_mtd_device(old->mtd); > > > > > > > > This looks wrong. See: > > > [...] > > > > deregister_mtd_blktrans() > > > > |_ mutex_lock(&mtd_table_mutex) > > > > |_ tr->remove_dev() -> inftl_remove_dev() > > > > |_ del_mtd_blktrans_dev() > > > > |_ put_mtd_device() > > > > |_ mutex_lock(&mtd_table_mutex) <--- AA deadlock > > > > > > What's more, this code in del_mtd_blktrans_dev() makes it obvious > > that > > > this hunk is wrong: > > > > > > int del_mtd_blktrans_dev(struct mtd_blktrans_dev *old) > > > { > > > unsigned long flags; > > > > > > if (mutex_trylock(&mtd_table_mutex)) { > > > mutex_unlock(&mtd_table_mutex); > > > BUG(); > > > } > > > ... > > > > > > So rather than a comment, the code is showing that it's a BUG() to > > not > > > be holding mtd_table_mutex already. > > > > Hello, > Thanks for your comments and for pointing this out. > Definitely yes.. we shouldn't change del_mtd_blktrans_dev(). > > > As an alternative to your patch, how about the following? > > I think it's the right way to go now. Can I get a 'Tested-by', or at least an 'Acked-by' for the patch? I tested it, but I don't think I can reproduce your original problem very easily. Brian -- 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/