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Code

regulator: core: Fix deadlock in create_regulator()

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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 cba6cfdc7c
("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: cba6cfdc7c ("regulator: core: Avoid lockdep reports when resolving supplies")
Fixes: eaa7995c52 ("regulator: core: avoid regulator_resolve_supply() race condition")
Signed-off-by: Ludvig Pärsson <ludvig.parsson@axis.com>
Link: https://patch.msgid.link/20250305-regulator_lockdep_fix-v1-1-ab938b12e790@axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Ludvig Pärsson 2025-03-05 17:05:04 +01:00 committed by Mark Brown
parent 7eb172143d
commit 1c81a8c78a
No known key found for this signature in database
GPG Key ID: 24D68B725D5487D0
1 changed files with 43 additions and 33 deletions
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76
drivers/regulator/core.c
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@ -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;