[PATCH 5.10 20/54] regulator: core: avoid regulator_resolve_supply() race condition

Greg Kroah-Hartman
2021-02-11T16:27:33Z

From: David Collins <collinsd@codeaurora.org>

[ Upstream commit eaa7995c529b54d68d97a30f6344cc6ca2f214a7 ]

The final step in regulator_register() is to call
regulator_resolve_supply() for each registered regulator
(including the one in the process of being registered). The
regulator_resolve_supply() function first checks if rdev->supply
is NULL, then it performs various steps to try to find the supply.
If successful, rdev->supply is set inside of set_supply().

This procedure can encounter a race condition if two concurrent
tasks call regulator_register() near to each other on separate CPUs
and one of the regulators has rdev->supply_name specified. There
is currently nothing guaranteeing atomicity between the rdev->supply
check and set steps. Thus, both tasks can observe rdev->supply==NULL
in their regulator_resolve_supply() calls. This then results in
both creating a struct regulator for the supply. One ends up
actually stored in rdev->supply and the other is lost (though still
present in the supply's consumer_list).

Here is a kernel log snippet showing the issue:

[ 12.421768] gpu_cc_gx_gdsc: supplied by pm8350_s5_level
[ 12.425854] gpu_cc_gx_gdsc: supplied by pm8350_s5_level
[ 12.429064] debugfs: Directory 'regulator.4-SUPPLY' with parent
'17a00000.rsc:rpmh-regulator-gfxlvl-pm8350_s5_level'
already present!

Avoid this race condition by holding the rdev->mutex lock inside
of regulator_resolve_supply() while checking and setting
rdev->supply.

Signed-off-by: David Collins <collinsd@codeaurora.org>
Link: https://lore.kernel.org/r/1610068562-4410-1-git-send-email-collinsd@codeaurora.org
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/regulator/core.c | 39 ++++++++++++++++++++++++++++-----------
1 file changed, 28 insertions(+), 11 deletions(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 42bbd99a36acf..2c31f04ff950f 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -1813,23 +1813,34 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
{
struct regulator_dev *r;
struct device *dev = rdev->dev.parent;
- int ret;
+ int ret = 0;

/* No supply to resolve? */
if (!rdev->supply_name)
return 0;

- /* Supply already resolved? */
+ /* Supply already resolved? (fast-path without locking contention) */
if (rdev->supply)
return 0;

+ /*
+ * Recheck rdev->supply with rdev->mutex lock held to avoid a race
+ * between rdev->supply null check and setting rdev->supply in
+ * set_supply() from concurrent tasks.
+ */
+ regulator_lock(rdev);
+
+ /* Supply just resolved by a concurrent task? */
+ if (rdev->supply)
+ goto out;
+
r = regulator_dev_lookup(dev, rdev->supply_name);
if (IS_ERR(r)) {
ret = PTR_ERR(r);

/* Did the lookup explicitly defer for us? */
if (ret == -EPROBE_DEFER)
- return ret;
+ goto out;

if (have_full_constraints()) {
r = dummy_regulator_rdev;
@@ -1837,15 +1848,18 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
} else {
dev_err(dev, "Failed to resolve %s-supply for %s\n",
rdev->supply_name, rdev->desc->name);
- return -EPROBE_DEFER;
+ ret = -EPROBE_DEFER;
+ goto out;
}
}

if (r == rdev) {
dev_err(dev, "Supply for %s (%s) resolved to itself\n",
rdev->desc->name, rdev->supply_name);
- if (!have_full_constraints())
- return -EINVAL;
+ if (!have_full_constraints()) {
+ ret = -EINVAL;
+ goto out;
+ }
r = dummy_regulator_rdev;
get_device(&r->dev);
}
@@ -1859,7 +1873,8 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
if (r->dev.parent && r->dev.parent != rdev->dev.parent) {
if (!device_is_bound(r->dev.parent)) {
put_device(&r->dev);
- return -EPROBE_DEFER;
+ ret = -EPROBE_DEFER;
+ goto out;
}
}

@@ -1867,13 +1882,13 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
ret = regulator_resolve_supply(r);
if (ret < 0) {
put_device(&r->dev);
- return ret;
+ goto out;
}

ret = set_supply(rdev, r);
if (ret < 0) {
put_device(&r->dev);
- return ret;
+ goto out;
}

/*
@@ -1886,11 +1901,13 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
if (ret < 0) {
_regulator_put(rdev->supply);
rdev->supply = NULL;
- return ret;
+ goto out;
}
}

- return 0;
+out:
+ regulator_unlock(rdev);
+ return ret;
}

/* Internal regulator request function */
--
2.27.0