[PATCH 6.12.y] hwmon: (pmbus/adm1266) serialize NVMEM blackbox read with pmbus_lock

[Sasha Levin <sashal@kernel.org>]

From: Abdurrahman Hussain <abdurrahman@nexthop.ai>

[ Upstream commit 9f1dd8f9491eb840cbea7ffdf4cad031e25f8ae0 ]

adm1266_nvmem_read() is the reg_read callback the NVMEM core invokes
when userspace reads /sys/bus/nvmem/devices/.../nvmem on this chip.
On the first byte of every read it does a memset of data->dev_mem,
walks the device blackbox through adm1266_nvmem_read_blackbox()
(which issues a chain of PMBus block transactions), and then memcpys
the refreshed buffer out to userspace.  None of that runs under
pmbus_lock today.

Two consequences:

  - The PMBus traffic the refresh issues is not serialised against
    pmbus_core's own multi-step PAGE+register sequences.  A paged
    hwmon attribute read from another thread can land between a
    PAGE write and the paged read in either direction and corrupt
    one side's view of the device state machine.

  - The NVMEM core does not serialise concurrent reg_read calls, so
    two userspace readers racing at offset 0 can interleave the
    memset of data->dev_mem with another reader's
    adm1266_nvmem_read_blackbox() refill or memcpy out, returning
    torn data to userspace.

Take pmbus_lock at the top of adm1266_nvmem_read() via the
scope-based guard().  Patch 5 of this series moves
adm1266_config_nvmem() past pmbus_do_probe() so the lock is
guaranteed to be live before the callback is reachable from
userspace.

Fixes: 15609d189302 ("hwmon: (pmbus/adm1266) read blackbox")
Cc: stable@vger.kernel.org
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
Link: https://lore.kernel.org/r/20260518-adm1266-gpio-fixes-v3-7-e425e4f88139@nexthop.ai
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
[ changed `guard(pmbus_lock)(data->client)` to explicit `pmbus_lock_interruptible()`/`pmbus_unlock()` ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/hwmon/pmbus/adm1266.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/hwmon/pmbus/adm1266.c b/drivers/hwmon/pmbus/adm1266.c
index 2c4d94cc872943..69ec25d6f48dac 100644
--- a/drivers/hwmon/pmbus/adm1266.c
+++ b/drivers/hwmon/pmbus/adm1266.c
@@ -383,18 +383,25 @@ static int adm1266_nvmem_read(void *priv, unsigned int offset, void *val, size_t
 	if (offset + bytes > data->nvmem_config.size)
 		return -EINVAL;
 
+	ret = pmbus_lock_interruptible(data->client);
+	if (ret)
+		return ret;
+
 	if (offset == 0) {
 		memset(data->dev_mem, 0, data->nvmem_config.size);
 
 		ret = adm1266_nvmem_read_blackbox(data, data->dev_mem);
 		if (ret) {
 			dev_err(&data->client->dev, "Could not read blackbox!");
+			pmbus_unlock(data->client);
 			return ret;
 		}
 	}
 
 	memcpy(val, data->dev_mem + offset, bytes);
 
+	pmbus_unlock(data->client);
+
 	return 0;
 }
 
-- 
2.53.0