If kernel is compiled with CONFIG_PROVE_LOCKING the
validator raises an error when a multiplexer is removed
via sysfs and sub-clients are connected to it. This is a
false positive.
Documentation/lockdep-design.txt recommends to handle this
via calls to mutex_lock_nested().
Based on an earlier fix from Michael Lawnick.
Note that the extra code resolves to nothing unless
CONFIG_DEBUG_LOCK_ALLOC=y.
Signed-off-by: Jean Delvare <khali@xxxxxxxxxxxx>
Cc: Michael Lawnick <ml.lawnick@xxxxxx>
---
Note that I still get a complaint from lockdep even with this patch,
but it's a different one... Related to sysfs, not something for me:
=============================================
[ INFO: possible recursive locking detected ]
3.6.0-rc4 #48 Not tainted
---------------------------------------------
bash/13695 is trying to acquire lock:
(s_active#276){++++.+}, at: [<ffffffff811ed361>] sysfs_addrm_finish+0x31/0x60
but task is already holding lock:
(s_active#276){++++.+}, at: [<ffffffff811eb7d8>] sysfs_write_file+0xe8/0x170
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(s_active#276);
lock(s_active#276);
*** DEADLOCK ***
May be due to missing lock nesting notation
4 locks held by bash/13695:
#0: (&buffer->mutex){+.+.+.}, at: [<ffffffff811eb72f>] sysfs_write_file+0x3f/0x170
#1: (s_active#276){++++.+}, at: [<ffffffff811eb7d8>] sysfs_write_file+0xe8/0x170
#2: (&adap->userspace_clients_lock){+.+.+.}, at: [<ffffffff81479b7f>] i2c_sysfs_delete_device+0xcf/0x210
#3: (&__lockdep_no_validate__){......}, at: [<ffffffff813c7e81>] device_release_driver+0x21/0x40
I guess it's a false positive too, as I did not actually get a deadlock.
drivers/i2c/i2c-core.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
--- linux-3.6-rc4.orig/drivers/i2c/i2c-core.c 2012-09-07 17:53:31.851926473 +0200
+++ linux-3.6-rc4/drivers/i2c/i2c-core.c 2012-09-07 18:55:36.562869851 +0200
@@ -636,6 +636,16 @@ static void i2c_adapter_dev_release(stru
complete(&adap->dev_released);
}
+static unsigned int i2c_adapter_depth(struct i2c_adapter *adapter)
+{
+ unsigned int depth = 0;
+
+ while ((adapter = i2c_parent_is_i2c_adapter(adapter)))
+ depth++;
+
+ return depth;
+}
+
/*
* Let users instantiate I2C devices through sysfs. This can be used when
* platform initialization code doesn't contain the proper data for
@@ -726,7 +736,8 @@ i2c_sysfs_delete_device(struct device *d
/* Make sure the device was added through sysfs */
res = -ENOENT;
- mutex_lock(&adap->userspace_clients_lock);
+ mutex_lock_nested(&adap->userspace_clients_lock,
+ i2c_adapter_depth(adap));
list_for_each_entry_safe(client, next, &adap->userspace_clients,
detected) {
if (client->addr == addr) {
@@ -1073,7 +1084,8 @@ int i2c_del_adapter(struct i2c_adapter *
return res;
/* Remove devices instantiated from sysfs */
- mutex_lock(&adap->userspace_clients_lock);
+ mutex_lock_nested(&adap->userspace_clients_lock,
+ i2c_adapter_depth(adap));
list_for_each_entry_safe(client, next, &adap->userspace_clients,
detected) {
dev_dbg(&adap->dev, "Removing %s at 0x%x\n", client->name,
--
Jean Delvare
--
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