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([2620:15c:2cd:203:5cdc:422c:7b28:ebb5]) by smtp.gmail.com with ESMTPSA id b11-v6sm36529501pgi.10.2018.11.06.09.22.24 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 06 Nov 2018 09:22:25 -0800 (PST) Message-ID: <1541524943.196084.178.camel@acm.org> Subject: Re: [driver-core PATCH v5 4/9] driver core: Move async_synchronize_full call From: Bart Van Assche To: Alexander Duyck , linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org Cc: linux-nvdimm@lists.01.org, tj@kernel.org, akpm@linux-foundation.org, linux-pm@vger.kernel.org, jiangshanlai@gmail.com, rafael@kernel.org, len.brown@intel.com, pavel@ucw.cz, zwisler@kernel.org, dan.j.williams@intel.com, dave.jiang@intel.com Date: Tue, 06 Nov 2018 09:22:23 -0800 In-Reply-To: References: <154145223352.29224.8912797012647157172.stgit@ahduyck-desk1.jf.intel.com> <154145231976.29224.39638353241256116.stgit@ahduyck-desk1.jf.intel.com> <1541466289.196084.176.camel@acm.org> Content-Type: text/plain; charset="UTF-7" X-Mailer: Evolution 3.26.2-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2018-11-06 at 08:18 -0800, Alexander Duyck wrote: +AD4 On Mon, 2018-11-05 at 17:04 -0800, Bart Van Assche wrote: +AD4 +AD4 On Mon, 2018-11-05 at 13:11 -0800, Alexander Duyck wrote: +AD4 +AD4 +AD4 This patch moves the async+AF8-synchronize+AF8-full call out of +AD4 +AD4 +AD4 +AF8AXw-device+AF8-release+AF8-driver and into driver+AF8-detach. +AD4 +AD4 +AD4 +AD4 +AD4 +AD4 The idea behind this is that the async+AF8-synchronize+AF8-full call will only +AD4 +AD4 +AD4 guarantee that any existing async operations are flushed. This doesn't do +AD4 +AD4 +AD4 anything to guarantee that a hotplug event that may occur while we are +AD4 +AD4 +AD4 doing the release of the driver will not be asynchronously scheduled. +AD4 +AD4 +AD4 +AD4 +AD4 +AD4 By moving this into the driver+AF8-detach path we can avoid potential deadlocks +AD4 +AD4 +AD4 as we aren't holding the device lock at this point and we should not have +AD4 +AD4 +AD4 the driver we want to flush loaded so the flush will take care of any +AD4 +AD4 +AD4 asynchronous events the driver we are detaching might have scheduled. +AD4 +AD4 +AD4 +AD4 +AD4 +AD4 Signed-off-by: Alexander Duyck +ADw-alexander.h.duyck+AEA-linux.intel.com+AD4 +AD4 +AD4 +AD4 --- +AD4 +AD4 +AD4 drivers/base/dd.c +AHw 6 +-+-+---- +AD4 +AD4 +AD4 1 file changed, 3 insertions(+-), 3 deletions(-) +AD4 +AD4 +AD4 +AD4 +AD4 +AD4 diff --git a/drivers/base/dd.c b/drivers/base/dd.c +AD4 +AD4 +AD4 index 76c40fe69463..e74cefeb5b69 100644 +AD4 +AD4 +AD4 --- a/drivers/base/dd.c +AD4 +AD4 +AD4 +-+-+- b/drivers/base/dd.c +AD4 +AD4 +AD4 +AEAAQA -975,9 +-975,6 +AEAAQA static void +AF8AXw-device+AF8-release+AF8-driver(struct device +ACo-dev, struct device +ACo-parent) +AD4 +AD4 +AD4 +AD4 +AD4 +AD4 drv +AD0 dev-+AD4-driver+ADs +AD4 +AD4 +AD4 if (drv) +AHs +AD4 +AD4 +AD4 - if (driver+AF8-allows+AF8-async+AF8-probing(drv)) +AD4 +AD4 +AD4 - async+AF8-synchronize+AF8-full()+ADs +AD4 +AD4 +AD4 - +AD4 +AD4 +AD4 while (device+AF8-links+AF8-busy(dev)) +AHs +AD4 +AD4 +AD4 +AF8AXw-device+AF8-driver+AF8-unlock(dev, parent)+ADs +AD4 +AD4 +AD4 +AD4 +AD4 +AD4 +AEAAQA -1087,6 +-1084,9 +AEAAQA void driver+AF8-detach(struct device+AF8-driver +ACo-drv) +AD4 +AD4 +AD4 struct device+AF8-private +ACo-dev+AF8-prv+ADs +AD4 +AD4 +AD4 struct device +ACo-dev+ADs +AD4 +AD4 +AD4 +AD4 +AD4 +AD4 +- if (driver+AF8-allows+AF8-async+AF8-probing(drv)) +AD4 +AD4 +AD4 +- async+AF8-synchronize+AF8-full()+ADs +AD4 +AD4 +AD4 +- +AD4 +AD4 +AD4 for (+ADsAOw) +AHs +AD4 +AD4 +AD4 spin+AF8-lock(+ACY-drv-+AD4-p-+AD4-klist+AF8-devices.k+AF8-lock)+ADs +AD4 +AD4 +AD4 if (list+AF8-empty(+ACY-drv-+AD4-p-+AD4-klist+AF8-devices.k+AF8-list)) +AHs +AD4 +AD4 +AD4 +AD4 Have you considered to move that async+AF8-synchronize+AF8-full() call into +AD4 +AD4 bus+AF8-remove+AF8-driver()? Verifying the correctness of this patch requires to +AD4 +AD4 check whether the async+AF8-synchronize+AF8-full() comes after the +AD4 +AD4 klist+AF8-remove(+ACY-drv-+AD4-p-+AD4-knode+AF8-bus) call. That verification is easier when +AD4 +AD4 the async+AF8-synchronize+AF8-full() call occurs in bus+AF8-remove+AF8-driver() instead +AD4 +AD4 of in driver+AF8-detach(). +AD4 +AD4 I considered it, however it ends up with things being more symmetric to +AD4 have use take care of synchronizing things in driver+AF8-detach since after +AD4 this patch set we are scheduling thing asynchronously in driver+AF8-attach. +AD4 +AD4 Also I don't think it would be any great risk simply because calling +AD4 driver+AF8-detach with the driver still associated with the bus would be a +AD4 blatent error as it could easily lead to issues where you unbind a +AD4 driver but have it get hotplugged to a device while that is going on. Thanks for the additional clarification. Since I'm fine with this patch: Reviewed-by: Bart Van Assche +ADw-bvanassche+AEA-acm.org+AD4