From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-x242.google.com (mail-pf0-x242.google.com [IPv6:2607:f8b0:400e:c00::242]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3xBMdJ5kRPzDrFM for ; Tue, 18 Jul 2017 11:14:28 +1000 (AEST) Received: by mail-pf0-x242.google.com with SMTP id q85so703482pfq.2 for ; Mon, 17 Jul 2017 18:14:28 -0700 (PDT) Message-ID: <1500340459.2475.6.camel@gmail.com> Subject: Re: [PATCH v3 02/10] mtd: powernv_flash: Lock around concurrent access to OPAL From: Cyril Bur To: Balbir Singh , linuxppc-dev@lists.ozlabs.org, linux-mtd@lists.infradead.org Cc: stewart@linux.vnet.ibm.com, alistair@popple.id.au, dwmw2@infradead.org, rlippert@google.com Date: Tue, 18 Jul 2017 11:14:19 +1000 In-Reply-To: <1500283754.8256.11.camel@gmail.com> References: <20170712042304.19745-1-cyrilbur@gmail.com> <20170712042304.19745-3-cyrilbur@gmail.com> <1500276875.8256.3.camel@gmail.com> <1500278150.29477.1.camel@gmail.com> <1500283754.8256.11.camel@gmail.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 2017-07-17 at 19:29 +1000, Balbir Singh wrote: > On Mon, 2017-07-17 at 17:55 +1000, Cyril Bur wrote: > > On Mon, 2017-07-17 at 17:34 +1000, Balbir Singh wrote: > > > On Wed, 2017-07-12 at 14:22 +1000, Cyril Bur wrote: > > > > OPAL can only manage one flash access at a time and will return an > > > > OPAL_BUSY error for each concurrent access to the flash. The simplest > > > > way to prevent this from happening is with a mutex. > > > > > > > > Signed-off-by: Cyril Bur > > > > --- > > > > > > Should the mutex_lock() be mutex_lock_interruptible()? Are we OK waiting on > > > the mutex while other operations with the lock are busy? > > > > > > > This is a good question. My best interpretation is that > > _interruptible() should be used when you'll only be coming from a user > > context. Which is mostly true for this driver, however, MTD does > > provide kernel interfaces, so I was hesitant, there isn't a great deal > > of use of _interruptible() in drivers/mtd. > > > > Thoughts? > > What are the kernel interfaces (I have not read through mtd in detail)? > I would still like to see us not blocked in mutex_lock() across threads > for parallel calls, one option is to use mutex_trylock() and return if > someone already holds the mutex with -EBUSY, but you'll need to evaluate > what that means for every call. > Yeah maybe mutex_trylock() is the way to go, thinking quickly, I don't see how it could be a problem for userspace using powernv_flash. I'm honestly not too sure about the depths of the mtd kernel interfaces but I've seen a tonne of cool stuff you could do, hence my reluctance to go with _interruptible() Cyril > Balbir Singh. >