Messages in this thread | | | From | "Cantavenera, Giuseppe (EXT-Other - DE/Ulm)" <> | Subject | RE: [PATCH] mtd: fix: avoid race condition when accessing mtd->usecount | Date | Mon, 11 May 2015 07:44:26 +0000 |
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> -----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.
Thanks! Giuseppe
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