Messages in this thread | | | From | Chen-Yu Tsai <> | Date | Mon, 9 Jan 2023 15:35:08 +0800 | Subject | Re: [PATCH] platform/chromeos: cros_ec: Use per-device lockdep key |
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On Mon, Jan 9, 2023 at 3:30 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote: > > On Mon, Jan 09, 2023 at 02:19:38PM +0800, Chen-Yu Tsai wrote: > > On Mon, Jan 9, 2023 at 1:46 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote: > > > > > > On Sat, Jan 07, 2023 at 01:43:57PM +0800, Chen-Yu Tsai wrote: > > > > On Fri, Jan 6, 2023 at 5:08 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote: > > > > > > > > > > On Fri, Jan 06, 2023 at 12:55:37PM +0800, Chen-Yu Tsai wrote: > > > > > > Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to > > > > > > the following lock sequences: > > > > > > > > > > > > 1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock) > > > > > > 2. lock(&ec_dev->lock); lock(prepare_lock); > > > > > > > > > > > > The actual dependency chains are much longer. The shortened version > > > > > > looks somewhat like: > > > > > > > > > > > > 1. cros-ec-rpmsg on mtk-scp > > > > > > ec_dev->lock -> prepare_lock > > > > > > 2. In rt5682_i2c_probe() on native I2C bus: > > > > > > prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock > > > > > > 3. In rt5682_i2c_probe() on native I2C bus: > > > > > > regmap->lock -> i2c_adapter->bus_lock > > > > > > 4. In sbs_probe() on cros-ec-i2c (passthrough) I2C bus on cros-ec > > > > > > i2c_adapter->bus_lock -> ec_dev->lock > > > > > > > > > > > > While lockdep is correct that the shared lockdep classes have a circular > > > > > > dependency, it is bogus because > > > > > > > > > > > > a) 2+3 happen on a native I2C bus > > > > > > b) 4 happens on the actual EC on ChromeOS devices > > > > > > c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just > > > > > > happen to expose a cros-ec interface, but do not have a passthrough > > > > > > I2C bus > > > > > > > > > > > > In short, the "dependencies" are actually on different devices. > > > > > > > > > > Path of 4 looks weird to me. > > > > > > > > > > Could you point out where sbs_probe() gets to acquire ec_dev->lock? > > > > > > > > sbs_probe() calls sbs_get_battery_presence_and_health(), which > > > > > > > > -> does an I2C transfer. This SBS instance is connected on the I2C bus > > > > on the EC, so the I2C transfer > > > > > > > > -> acquires i2c_adapter->bus_lock, and > > > > > > I see. > > > > > > Another question: the i2c_adapter here should be different from the native > > > I2C bus in 2 and 3. Did they really form the circular dependencies? > > > > That's why it's a false positive. lockdep normally doesn't track individual > > instances, only classes of locks. The class is declared as part of the > > mutex_init() macro. > > Is the following understanding correct: > It has 2 ways to break the "fake" circular dependencies: separate lockdep key > for i2c_adapter vs. ec_dev. The patch adopts the latter one because it has > limited impact for other I2C-related drivers.
That's correct.
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