2020-08-10 20:10:44

by Michał Mirosław

Subject: [RFC PATCH 2/3] regulator: push enable_gpio allocation out from under regulator_list_mutex

Move another allocation out of regulator_list_mutex-protected region, as
reclaim might want to take the same lock.

WARNING: possible circular locking dependency detected
5.7.13+ #534 Not tainted
------------------------------------------------------
kswapd0/383 is trying to acquire lock:
c0e5d920 (regulator_list_mutex){+.+.}-{3:3}, at: regulator_lock_dependent+0x54/0x2c0

but task is already holding lock:
c0e38518 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x50

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (fs_reclaim){+.+.}-{0:0}:
fs_reclaim_acquire.part.11+0x40/0x50
fs_reclaim_acquire+0x24/0x28
kmem_cache_alloc_trace+0x40/0x1e8
regulator_register+0x384/0x1630
devm_regulator_register+0x50/0x84
reg_fixed_voltage_probe+0x248/0x35c
[...]
other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(fs_reclaim);
lock(regulator_list_mutex);
lock(fs_reclaim);
lock(regulator_list_mutex);

*** DEADLOCK ***
[...]
2 locks held by kswapd0/383:
#0: c0e38518 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x50
#1: cb70e5e0 (hctx->srcu){....}-{0:0}, at: hctx_lock+0x60/0xb8
[...]

Fixes: 541d052d7215 ("regulator: core: Only support passing enable GPIO descriptors")
[this commit only changes context]
Fixes: f8702f9e4aa7 ("regulator: core: Use ww_mutex for regulators locking")
[this is when the regulator_list_mutex was introduced in reclaim locking path]

Signed-off-by: Michał Mirosław <[email protected]>
---
drivers/regulator/core.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 915a727d8fc7..05c9657c99d9 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -2200,10 +2200,13 @@ EXPORT_SYMBOL_GPL(regulator_bulk_unregister_supply_alias);
static int regulator_ena_gpio_request(struct regulator_dev *rdev,
const struct regulator_config *config)
{
- struct regulator_enable_gpio *pin;
+ struct regulator_enable_gpio *pin, *new_pin;
struct gpio_desc *gpiod;

gpiod = config->ena_gpiod;
+ new_pin = kzalloc(sizeof(*new_pin), GFP_KERNEL);
+
+ mutex_lock(&regulator_list_mutex);

list_for_each_entry(pin, &regulator_ena_gpio_list, list) {
if (pin->gpiod == gpiod) {
@@ -2212,9 +2215,13 @@ static int regulator_ena_gpio_request(struct regulator_dev *rdev,
}
}

- pin = kzalloc(sizeof(struct regulator_enable_gpio), GFP_KERNEL);
- if (pin == NULL)
+ if (new_pin == NULL) {
+ mutex_unlock(&regulator_list_mutex);
return -ENOMEM;
+ }
+
+ pin = new_pin;
+ new_pin = NULL;

pin->gpiod = gpiod;
list_add(&pin->list, &regulator_ena_gpio_list);
@@ -2222,6 +2229,10 @@ static int regulator_ena_gpio_request(struct regulator_dev *rdev,
update_ena_gpio_to_rdev:
pin->request_count++;
rdev->ena_pin = pin;
+
+ mutex_unlock(&regulator_list_mutex);
+ kfree(new_pin);
+
return 0;
}

@@ -5098,9 +5109,7 @@ regulator_register(const struct regulator_desc *regulator_desc,
}

if (config->ena_gpiod) {
- mutex_lock(&regulator_list_mutex);
ret = regulator_ena_gpio_request(rdev, config);
- mutex_unlock(&regulator_list_mutex);
if (ret != 0) {
rdev_err(rdev, "Failed to request enable GPIO: %d\n",
ret);
--
2.20.1