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regulator: core: avoid regulator_resolve_supply() race condition

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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>
This commit is contained in:
David Collins 2021-01-07 17:16:02 -08:00 committed by Mark Brown
parent 36836f5b37
commit eaa7995c52
No known key found for this signature in database
GPG Key ID: 24D68B725D5487D0
1 changed files with 28 additions and 11 deletions
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39
drivers/regulator/core.c
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@ -1813,23 +1813,34 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
{ {
struct regulator_dev *r; struct regulator_dev *r;
struct device *dev = rdev->dev.parent; struct device *dev = rdev->dev.parent;
int ret; int ret = 0;
/* No supply to resolve? */ /* No supply to resolve? */
if (!rdev->supply_name) if (!rdev->supply_name)
return 0; return 0;
/* Supply already resolved? */ /* Supply already resolved? (fast-path without locking contention) */
if (rdev->supply) if (rdev->supply)
return 0; 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); r = regulator_dev_lookup(dev, rdev->supply_name);
if (IS_ERR(r)) { if (IS_ERR(r)) {
ret = PTR_ERR(r); ret = PTR_ERR(r);
/* Did the lookup explicitly defer for us? */ /* Did the lookup explicitly defer for us? */
if (ret == -EPROBE_DEFER) if (ret == -EPROBE_DEFER)
return ret; goto out;
if (have_full_constraints()) { if (have_full_constraints()) {
r = dummy_regulator_rdev; r = dummy_regulator_rdev;
@ -1837,15 +1848,18 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
} else { } else {
dev_err(dev, "Failed to resolve %s-supply for %s\n", dev_err(dev, "Failed to resolve %s-supply for %s\n",
rdev->supply_name, rdev->desc->name); rdev->supply_name, rdev->desc->name);
return -EPROBE_DEFER; ret = -EPROBE_DEFER;
goto out;
} }
} }
if (r == rdev) { if (r == rdev) {
dev_err(dev, "Supply for %s (%s) resolved to itself\n", dev_err(dev, "Supply for %s (%s) resolved to itself\n",
rdev->desc->name, rdev->supply_name); rdev->desc->name, rdev->supply_name);
if (!have_full_constraints()) if (!have_full_constraints()) {
return -EINVAL; ret = -EINVAL;
goto out;
}
r = dummy_regulator_rdev; r = dummy_regulator_rdev;
get_device(&r->dev); 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 (r->dev.parent && r->dev.parent != rdev->dev.parent) {
if (!device_is_bound(r->dev.parent)) { if (!device_is_bound(r->dev.parent)) {
put_device(&r->dev); 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); ret = regulator_resolve_supply(r);
if (ret < 0) { if (ret < 0) {
put_device(&r->dev); put_device(&r->dev);
return ret; goto out;
} }
ret = set_supply(rdev, r); ret = set_supply(rdev, r);
if (ret < 0) { if (ret < 0) {
put_device(&r->dev); put_device(&r->dev);
return ret; goto out;
} }
/* /*
@ -1886,11 +1901,13 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
if (ret < 0) { if (ret < 0) {
_regulator_put(rdev->supply); _regulator_put(rdev->supply);
rdev->supply = NULL; rdev->supply = NULL;
return ret; goto out;
} }
} }
return 0; out:
regulator_unlock(rdev);
return ret;
} }
/* Internal regulator request function */ /* Internal regulator request function */