Unverified Commit 1c81a8c7 authored by Ludvig Pärsson's avatar Ludvig Pärsson Committed by Mark Brown
Browse files

regulator: core: Fix deadlock in create_regulator() 



Currently, we are unnecessarily holding a regulator_ww_class_mutex lock
when creating debugfs entries for a newly created regulator. This was
brought up as a concern in the discussion in commit cba6cfdc
("regulator: core: Avoid lockdep reports when resolving supplies").

This causes the following lockdep splat after executing
`ls /sys/kernel/debug` on my platform:

  ======================================================
  WARNING: possible circular locking dependency detected
  5.15.167-axis9-devel #1 Tainted: G           O
  ------------------------------------------------------
  ls/2146 is trying to acquire lock:
  ffffff803a562918 (&mm->mmap_lock){++++}-{3:3}, at: __might_fault+0x40/0x88

  but task is already holding lock:
  ffffff80014497f8 (&sb->s_type->i_mutex_key#3){++++}-{3:3}, at: iterate_dir+0x50/0x1f4

  which lock already depends on the new lock.

  [...]

  Chain exists of:
    &mm->mmap_lock --> regulator_ww_class_mutex --> &sb->s_type->i_mutex_key#3

   Possible unsafe locking scenario:

         CPU0                    CPU1
         ----                    ----
    lock(&sb->s_type->i_mutex_key#3);
                                 lock(regulator_ww_class_mutex);
                                 lock(&sb->s_type->i_mutex_key#3);
    lock(&mm->mmap_lock);

   *** DEADLOCK ***

This lock dependency still exists on the latest kernel and using a newer
non-tainted kernel would still cause this problem.

Fix by moving sysfs symlinking and creation of debugfs entries to after
the release of the regulator lock.

Fixes: cba6cfdc ("regulator: core: Avoid lockdep reports when resolving supplies")
Fixes: eaa7995c ("regulator: core: avoid regulator_resolve_supply() race condition")
Signed-off-by: default avatarLudvig Pärsson <ludvig.parsson@axis.com>
Link: https://patch.msgid.link/20250305-regulator_lockdep_fix-v1-1-ab938b12e790@axis.com


Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent 7eb17214

drivers/regulator/core.c

+43 −33
Original line number Diff line number Diff line
@@ -1830,12 +1830,49 @@ static const struct file_operations constraint_flags_fops = { 


#define REG_STR_SIZE	64



static void link_and_create_debugfs(struct regulator *regulator, struct regulator_dev *rdev,

				    struct device *dev)

{

	int err = 0;



	if (dev) {

		regulator->dev = dev;



		/* Add a link to the device sysfs entry */

		err = sysfs_create_link_nowarn(&rdev->dev.kobj, &dev->kobj,

					       regulator->supply_name);

		if (err) {

			rdev_dbg(rdev, "could not add device link %s: %pe\n",

				 dev->kobj.name, ERR_PTR(err));

			/* non-fatal */

		}

	}



	if (err != -EEXIST) {

		regulator->debugfs = debugfs_create_dir(regulator->supply_name, rdev->debugfs);

		if (IS_ERR(regulator->debugfs)) {

			rdev_dbg(rdev, "Failed to create debugfs directory\n");

			regulator->debugfs = NULL;

		}

	}



	if (regulator->debugfs) {

		debugfs_create_u32("uA_load", 0444, regulator->debugfs,

				   &regulator->uA_load);

		debugfs_create_u32("min_uV", 0444, regulator->debugfs,

				   &regulator->voltage[PM_SUSPEND_ON].min_uV);

		debugfs_create_u32("max_uV", 0444, regulator->debugfs,

				   &regulator->voltage[PM_SUSPEND_ON].max_uV);

		debugfs_create_file("constraint_flags", 0444, regulator->debugfs,

				    regulator, &constraint_flags_fops);

	}

}



static struct regulator *create_regulator(struct regulator_dev *rdev,

					  struct device *dev,

					  const char *supply_name)

{

	struct regulator *regulator;

	int err = 0;



	lockdep_assert_held_once(&rdev->mutex.base);
@@ -1868,38 +1905,6 @@ static struct regulator *create_regulator(struct regulator_dev *rdev, 


	list_add(&regulator->list, &rdev->consumer_list);



	if (dev) {

		regulator->dev = dev;



		/* Add a link to the device sysfs entry */

		err = sysfs_create_link_nowarn(&rdev->dev.kobj, &dev->kobj,

					       supply_name);

		if (err) {

			rdev_dbg(rdev, "could not add device link %s: %pe\n",

				  dev->kobj.name, ERR_PTR(err));

			/* non-fatal */

		}

	}



	if (err != -EEXIST) {

		regulator->debugfs = debugfs_create_dir(supply_name, rdev->debugfs);

		if (IS_ERR(regulator->debugfs)) {

			rdev_dbg(rdev, "Failed to create debugfs directory\n");

			regulator->debugfs = NULL;

		}

	}



	if (regulator->debugfs) {

		debugfs_create_u32("uA_load", 0444, regulator->debugfs,

				   &regulator->uA_load);

		debugfs_create_u32("min_uV", 0444, regulator->debugfs,

				   &regulator->voltage[PM_SUSPEND_ON].min_uV);

		debugfs_create_u32("max_uV", 0444, regulator->debugfs,

				   &regulator->voltage[PM_SUSPEND_ON].max_uV);

		debugfs_create_file("constraint_flags", 0444, regulator->debugfs,

				    regulator, &constraint_flags_fops);

	}



	/*

	 * Check now if the regulator is an always on regulator - if

	 * it is then we don't need to do nearly so much work for
@@ -2133,6 +2138,9 @@ static int regulator_resolve_supply(struct regulator_dev *rdev) 


	regulator_unlock_two(rdev, r, &ww_ctx);



	/* rdev->supply was created in set_supply() */

	link_and_create_debugfs(rdev->supply, r, &rdev->dev);



	/*

	 * In set_machine_constraints() we may have turned this regulator on

	 * but we couldn't propagate to the supply if it hadn't been resolved
@@ -2271,6 +2279,8 @@ struct regulator *_regulator_get_common(struct regulator_dev *rdev, struct devic 
		return regulator;

	}



	link_and_create_debugfs(regulator, rdev, dev);



	rdev->open_count++;

	if (get_type == EXCLUSIVE_GET) {

		rdev->exclusive = 1;