From: Douglas Anderson dianders@chromium.org
[ Upstream commit cba6cfdc7c3f1516f0d08ddfb24e689af0932573 ]
An automated bot told me that there was a potential lockdep problem with regulators. This was on the chromeos-5.15 kernel, but I see nothing that would be different downstream compared to upstream. The bot said: ============================================ WARNING: possible recursive locking detected 5.15.104-lockdep-17461-gc1e499ed6604 #1 Not tainted -------------------------------------------- kworker/u16:4/115 is trying to acquire lock: ffffff8083110170 (regulator_ww_class_mutex){+.+.}-{3:3}, at: create_regulator+0x398/0x7ec
but task is already holding lock: ffffff808378e170 (regulator_ww_class_mutex){+.+.}-{3:3}, at: ww_mutex_trylock+0x3c/0x7b8
other info that might help us debug this: Possible unsafe locking scenario:
CPU0 ---- lock(regulator_ww_class_mutex); lock(regulator_ww_class_mutex);
*** DEADLOCK ***
May be due to missing lock nesting notation
4 locks held by kworker/u16:4/115: #0: ffffff808006a948 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x520/0x1348 #1: ffffffc00e0a7cc0 ((work_completion)(&entry->work)){+.+.}-{0:0}, at: process_one_work+0x55c/0x1348 #2: ffffff80828a2260 (&dev->mutex){....}-{3:3}, at: __device_attach_async_helper+0xd0/0x2a4 #3: ffffff808378e170 (regulator_ww_class_mutex){+.+.}-{3:3}, at: ww_mutex_trylock+0x3c/0x7b8
stack backtrace: CPU: 2 PID: 115 Comm: kworker/u16:4 Not tainted 5.15.104-lockdep-17461-gc1e499ed6604 #1 9292e52fa83c0e23762b2b3aa1bacf5787a4d5da Hardware name: Google Quackingstick (rev0+) (DT) Workqueue: events_unbound async_run_entry_fn Call trace: dump_backtrace+0x0/0x4ec show_stack+0x34/0x50 dump_stack_lvl+0xdc/0x11c dump_stack+0x1c/0x48 __lock_acquire+0x16d4/0x6c74 lock_acquire+0x208/0x750 __mutex_lock_common+0x11c/0x11f8 ww_mutex_lock+0xc0/0x440 create_regulator+0x398/0x7ec regulator_resolve_supply+0x654/0x7c4 regulator_register_resolve_supply+0x30/0x120 class_for_each_device+0x1b8/0x230 regulator_register+0x17a4/0x1f40 devm_regulator_register+0x60/0xd0 reg_fixed_voltage_probe+0x728/0xaec platform_probe+0x150/0x1c8 really_probe+0x274/0xa20 __driver_probe_device+0x1dc/0x3f4 driver_probe_device+0x78/0x1c0 __device_attach_driver+0x1ac/0x2c8 bus_for_each_drv+0x11c/0x190 __device_attach_async_helper+0x1e4/0x2a4 async_run_entry_fn+0xa0/0x3ac process_one_work+0x638/0x1348 worker_thread+0x4a8/0x9c4 kthread+0x2e4/0x3a0 ret_from_fork+0x10/0x20
The problem was first reported soon after we made many of the regulators probe asynchronously, though nothing I've seen implies that the problems couldn't have also happened even without that.
I haven't personally been able to reproduce the lockdep issue, but the issue does look somewhat legitimate. Specifically, it looks like in regulator_resolve_supply() we are holding a "rdev" lock while calling set_supply() -> create_regulator() which grabs the lock of a _different_ "rdev" (the one for our supply). This is not necessarily safe from a lockdep perspective since there is no documented ordering between these two locks.
In reality, we should always be locking a regulator before the supplying regulator, so I don't expect there to be any real deadlocks in practice. However, the regulator framework in general doesn't express this to lockdep.
Let's fix the issue by simply grabbing the two locks involved in the same way we grab multiple locks elsewhere in the regulator framework: using the "wound/wait" mechanisms.
Fixes: eaa7995c529b ("regulator: core: avoid regulator_resolve_supply() race condition") Signed-off-by: Douglas Anderson dianders@chromium.org Link: https://lore.kernel.org/r/20230329143317.RFC.v2.2.I30d8e1ca10cfbe5403884cdd1... Signed-off-by: Mark Brown broonie@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/regulator/core.c | 91 ++++++++++++++++++++++++++++++++++++---- 1 file changed, 83 insertions(+), 8 deletions(-)
diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c index 48db0735e3dba..9ddb80d10dee3 100644 --- a/drivers/regulator/core.c +++ b/drivers/regulator/core.c @@ -206,6 +206,78 @@ static void regulator_unlock(struct regulator_dev *rdev) mutex_unlock(®ulator_nesting_mutex); }
+/** + * regulator_lock_two - lock two regulators + * @rdev1: first regulator + * @rdev2: second regulator + * @ww_ctx: w/w mutex acquire context + * + * Locks both rdevs using the regulator_ww_class. + */ +static void regulator_lock_two(struct regulator_dev *rdev1, + struct regulator_dev *rdev2, + struct ww_acquire_ctx *ww_ctx) +{ + struct regulator_dev *tmp; + int ret; + + ww_acquire_init(ww_ctx, ®ulator_ww_class); + + /* Try to just grab both of them */ + ret = regulator_lock_nested(rdev1, ww_ctx); + WARN_ON(ret); + ret = regulator_lock_nested(rdev2, ww_ctx); + if (ret != -EDEADLOCK) { + WARN_ON(ret); + goto exit; + } + + while (true) { + /* + * Start of loop: rdev1 was locked and rdev2 was contended. + * Need to unlock rdev1, slowly lock rdev2, then try rdev1 + * again. + */ + regulator_unlock(rdev1); + + ww_mutex_lock_slow(&rdev2->mutex, ww_ctx); + rdev2->ref_cnt++; + rdev2->mutex_owner = current; + ret = regulator_lock_nested(rdev1, ww_ctx); + + if (ret == -EDEADLOCK) { + /* More contention; swap which needs to be slow */ + tmp = rdev1; + rdev1 = rdev2; + rdev2 = tmp; + } else { + WARN_ON(ret); + break; + } + } + +exit: + ww_acquire_done(ww_ctx); +} + +/** + * regulator_unlock_two - unlock two regulators + * @rdev1: first regulator + * @rdev2: second regulator + * @ww_ctx: w/w mutex acquire context + * + * The inverse of regulator_lock_two(). + */ + +static void regulator_unlock_two(struct regulator_dev *rdev1, + struct regulator_dev *rdev2, + struct ww_acquire_ctx *ww_ctx) +{ + regulator_unlock(rdev2); + regulator_unlock(rdev1); + ww_acquire_fini(ww_ctx); +} + static bool regulator_supply_is_couple(struct regulator_dev *rdev) { struct regulator_dev *c_rdev; @@ -1583,8 +1655,8 @@ static int set_machine_constraints(struct regulator_dev *rdev)
/** * set_supply - set regulator supply regulator - * @rdev: regulator name - * @supply_rdev: supply regulator name + * @rdev: regulator (locked) + * @supply_rdev: supply regulator (locked)) * * Called by platform initialisation code to set the supply regulator for this * regulator. This ensures that a regulators supply will also be enabled by the @@ -1756,6 +1828,8 @@ static struct regulator *create_regulator(struct regulator_dev *rdev, struct regulator *regulator; int err = 0;
+ lockdep_assert_held_once(&rdev->mutex.base); + if (dev) { char buf[REG_STR_SIZE]; int size; @@ -1783,9 +1857,7 @@ static struct regulator *create_regulator(struct regulator_dev *rdev, regulator->rdev = rdev; regulator->supply_name = supply_name;
- regulator_lock(rdev); list_add(®ulator->list, &rdev->consumer_list); - regulator_unlock(rdev);
if (dev) { regulator->dev = dev; @@ -1951,6 +2023,7 @@ static int regulator_resolve_supply(struct regulator_dev *rdev) { struct regulator_dev *r; struct device *dev = rdev->dev.parent; + struct ww_acquire_ctx ww_ctx; int ret = 0;
/* No supply to resolve? */ @@ -2017,23 +2090,23 @@ static int regulator_resolve_supply(struct regulator_dev *rdev) * between rdev->supply null check and setting rdev->supply in * set_supply() from concurrent tasks. */ - regulator_lock(rdev); + regulator_lock_two(rdev, r, &ww_ctx);
/* Supply just resolved by a concurrent task? */ if (rdev->supply) { - regulator_unlock(rdev); + regulator_unlock_two(rdev, r, &ww_ctx); put_device(&r->dev); goto out; }
ret = set_supply(rdev, r); if (ret < 0) { - regulator_unlock(rdev); + regulator_unlock_two(rdev, r, &ww_ctx); put_device(&r->dev); goto out; }
- regulator_unlock(rdev); + regulator_unlock_two(rdev, r, &ww_ctx);
/* * In set_machine_constraints() we may have turned this regulator on @@ -2146,7 +2219,9 @@ struct regulator *_regulator_get(struct device *dev, const char *id, return regulator; }
+ regulator_lock(rdev); regulator = create_regulator(rdev, dev, id); + regulator_unlock(rdev); if (regulator == NULL) { regulator = ERR_PTR(-ENOMEM); module_put(rdev->owner);