From mboxrd@z Thu Jan 1 00:00:00 1970 From: Philipp Zabel Subject: Re: [PATCH v14 00/11] mux controller abstraction and iio/i2c muxes Date: Mon, 24 Apr 2017 12:52:59 +0200 Message-ID: <1493031179.2446.9.camel@pengutronix.de> References: <1493022995-16917-1-git-send-email-peda@axentia.se> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1493022995-16917-1-git-send-email-peda@axentia.se> Sender: linux-kernel-owner@vger.kernel.org To: Peter Rosin Cc: Jonathan Cameron , linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Wolfram Sang , Rob Herring , Mark Rutland , Hartmut Knaack , Lars-Peter Clausen , Peter Meerwald-Stadler , Jonathan Corbet , linux-i2c@vger.kernel.org, devicetree@vger.kernel.org, linux-iio@vger.kernel.org, linux-doc@vger.kernel.org, Andrew Morton , Colin Ian King , Paul Gortmaker , kernel@pengutronix.de List-Id: devicetree@vger.kernel.org On Mon, 2017-04-24 at 10:36 +0200, Peter Rosin wrote: > Hi! > > The big change since v13 is that the mux state is now locked with a mutex > instead of an rwsem. Other that that, it is mostly restructuring and doc > changes. There are a few other "real" changes as well, but those changes > feel kind of minor. I guess what I'm trying to say is that although the > list of changes for v14 is longish, it's still basically the same as last > time. I have hooked this up to the video-multiplexer and now I trigger the lockdep debug_check_no_locks_held error message when selecting the mux input from userspace: $ media-ctl --links "'imx6-mipi-csi2':1->'ipu1_csi0_mux':0[1]" [ 66.258368] [ 66.259919] ===================================== [ 66.265369] [ BUG: media-ctl/258 still has locks held! ] [ 66.270810] 4.11.0-rc8-20170424-1+ #1305 Not tainted [ 66.275863] ------------------------------------- [ 66.282158] 1 lock held by media-ctl/258: [ 66.286464] #0: (&mux->lock){+.+.+.}, at: [<8074a6c0>] mux_control_select+0x24/0x50 [ 66.294424] [ 66.294424] stack backtrace: [ 66.298980] CPU: 0 PID: 258 Comm: media-ctl Not tainted 4.11.0-rc8+ #1305 [ 66.306771] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree) [ 66.313334] Backtrace: [ 66.315858] [<8010e5a4>] (dump_backtrace) from [<8010e8ac>] (show_stack+0x20/0x24) [ 66.323473] r7:80e518d0 r6:80e518d0 r5:600d0013 r4:00000000 [ 66.329190] [<8010e88c>] (show_stack) from [<80496cf4>] (dump_stack+0xb0/0xdc) [ 66.336470] [<80496c44>] (dump_stack) from [<8017e404>] (debug_check_no_locks_held+0xb8/0xbc) [ 66.345043] r9:ae8566b8 r8:ad88dc84 r7:ad88df58 r6:ad88dc84 r5:ad88df58 r4:ae856400 [ 66.352837] [<8017e34c>] (debug_check_no_locks_held) from [<8012b258>] (do_exit+0x79c/0xcc8) [ 66.361321] [<8012aabc>] (do_exit) from [<8012d25c>] (do_group_exit+0x4c/0xcc) [ 66.368581] r7:000000f8 [ 66.371161] [<8012d210>] (do_group_exit) from [<8012d2fc>] (__wake_up_parent+0x0/0x30) [ 66.379120] r7:000000f8 r6:76f71798 r5:00000000 r4:00000001 [ 66.384837] [<8012d2dc>] (SyS_exit_group) from [<80109380>] (ret_fast_syscall+0x0/0x1c) That correctly warns that the media-ctl process caused the mux->lock to be locked and still held when the process exited. Do we need a usage counter based mechanism for muxes that are (indirectly) controlled from userspace? regards Philipp