[PATCH v3 05/36] thunderbolt: Take domain lock in switch sysfs attribute callbacks

Mika Westerberg
2019-03-28T12:40:52Z

switch_lock was introduced because it allowed serialization of device
authorization requests from userspace without need to take the big
domain lock (tb->lock). This was fine because device authorization with
ICM is just one command that is sent to the firmware. Now that we start
to handle all tunneling in the driver switch_lock is not enough because
we need to walk over the topology to establish paths.

For this reason drop switch_lock from the driver completely in favour of
big domain lock.

There is one complication, though. If userspace is waiting for the lock
in tb_switch_set_authorized(), it keeps the device_del() from removing
the sysfs attribute because it waits for active users to release the
attribute first which leads into following splat:

INFO: task kworker/u8:3:73 blocked for more than 61 seconds.
Tainted: G W 5.1.0-rc1+ #244
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u8:3 D12976 73 2 0x80000000
Workqueue: thunderbolt0 tb_handle_hotplug [thunderbolt]
Call Trace:
? __schedule+0x2e5/0x740
? _raw_spin_lock_irqsave+0x12/0x40
? prepare_to_wait_event+0xc5/0x160
schedule+0x2d/0x80
__kernfs_remove.part.17+0x183/0x1f0
? finish_wait+0x80/0x80
kernfs_remove_by_name_ns+0x4a/0x90
remove_files.isra.1+0x2b/0x60
sysfs_remove_group+0x38/0x80
sysfs_remove_groups+0x24/0x40
device_remove_attrs+0x3d/0x70
device_del+0x14c/0x360
device_unregister+0x15/0x50
tb_switch_remove+0x9e/0x1d0 [thunderbolt]
tb_handle_hotplug+0x119/0x5a0 [thunderbolt]
? process_one_work+0x1b7/0x420
process_one_work+0x1b7/0x420
worker_thread+0x37/0x380
? _raw_spin_unlock_irqrestore+0xf/0x30
? process_one_work+0x420/0x420
kthread+0x118/0x130
? kthread_create_on_node+0x60/0x60
ret_from_fork+0x35/0x40

We deal this by following what network stack did for some of their
attributes and use mutex_trylock() with restart_syscall(). This makes
userspace release the attribute allowing sysfs attribute removal to
progress before the write is restarted and eventually fail when the
attribute is removed.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
---
drivers/thunderbolt/switch.c | 45 +++++++++++++++---------------------
drivers/thunderbolt/tb.h | 3 +--
2 files changed, 20 insertions(+), 28 deletions(-)

diff --git a/drivers/thunderbolt/switch.c b/drivers/thunderbolt/switch.c
index 5c2c0201ae7f..7fa4ab076404 100644
--- a/drivers/thunderbolt/switch.c
+++ b/drivers/thunderbolt/switch.c
@@ -10,15 +10,13 @@
#include <linux/idr.h>
#include <linux/nvmem-provider.h>
#include <linux/pm_runtime.h>
+#include <linux/sched/signal.h>
#include <linux/sizes.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>

#include "tb.h"

-/* Switch authorization from userspace is serialized by this lock */
-static DEFINE_MUTEX(switch_lock);
-
/* Switch NVM support */

#define NVM_DEVID 0x05
@@ -254,8 +252,8 @@ static int tb_switch_nvm_write(void *priv, unsigned int offset, void *val,
struct tb_switch *sw = priv;
int ret = 0;

- if (mutex_lock_interruptible(&switch_lock))
- return -ERESTARTSYS;
+ if (!mutex_trylock(&sw->tb->lock))
+ return restart_syscall();

/*
* Since writing the NVM image might require some special steps,
@@ -275,7 +273,7 @@ static int tb_switch_nvm_write(void *priv, unsigned int offset, void *val,
memcpy(sw->nvm->buf + offset, val, bytes);

unlock:
- mutex_unlock(&switch_lock);
+ mutex_unlock(&sw->tb->lock);

return ret;
}
@@ -364,10 +362,7 @@ static int tb_switch_nvm_add(struct tb_switch *sw)
}
nvm->non_active = nvm_dev;

- mutex_lock(&switch_lock);
sw->nvm = nvm;
- mutex_unlock(&switch_lock);
-
return 0;

err_nvm_active:
@@ -384,10 +379,8 @@ static void tb_switch_nvm_remove(struct tb_switch *sw)
{
struct tb_switch_nvm *nvm;

- mutex_lock(&switch_lock);
nvm = sw->nvm;
sw->nvm = NULL;
- mutex_unlock(&switch_lock);

if (!nvm)
return;
@@ -698,8 +691,8 @@ static int tb_switch_set_authorized(struct tb_switch *sw, unsigned int val)
{
int ret = -EINVAL;

- if (mutex_lock_interruptible(&switch_lock))
- return -ERESTARTSYS;
+ if (!mutex_trylock(&sw->tb->lock))
+ return restart_syscall();

if (sw->authorized)
goto unlock;
@@ -742,7 +735,7 @@ static int tb_switch_set_authorized(struct tb_switch *sw, unsigned int val)
}

unlock:
- mutex_unlock(&switch_lock);
+ mutex_unlock(&sw->tb->lock);
return ret;
}

@@ -799,15 +792,15 @@ static ssize_t key_show(struct device *dev, struct device_attribute *attr,
struct tb_switch *sw = tb_to_switch(dev);
ssize_t ret;

- if (mutex_lock_interruptible(&switch_lock))
- return -ERESTARTSYS;
+ if (!mutex_trylock(&sw->tb->lock))
+ return restart_syscall();

if (sw->key)
ret = sprintf(buf, "%*phN\n", TB_SWITCH_KEY_SIZE, sw->key);
else
ret = sprintf(buf, "\n");

- mutex_unlock(&switch_lock);
+ mutex_unlock(&sw->tb->lock);
return ret;
}

@@ -824,8 +817,8 @@ static ssize_t key_store(struct device *dev, struct device_attribute *attr,
else if (hex2bin(key, buf, sizeof(key)))
return -EINVAL;

- if (mutex_lock_interruptible(&switch_lock))
- return -ERESTARTSYS;
+ if (!mutex_trylock(&sw->tb->lock))
+ return restart_syscall();

if (sw->authorized) {
ret = -EBUSY;
@@ -840,7 +833,7 @@ static ssize_t key_store(struct device *dev, struct device_attribute *attr,
}
}

- mutex_unlock(&switch_lock);
+ mutex_unlock(&sw->tb->lock);
return ret;
}
static DEVICE_ATTR(key, 0600, key_show, key_store);
@@ -886,8 +879,8 @@ static ssize_t nvm_authenticate_store(struct device *dev,
bool val;
int ret;

- if (mutex_lock_interruptible(&switch_lock))
- return -ERESTARTSYS;
+ if (!mutex_trylock(&sw->tb->lock))
+ return restart_syscall();

/* If NVMem devices are not yet added */
if (!sw->nvm) {
@@ -935,7 +928,7 @@ static ssize_t nvm_authenticate_store(struct device *dev,
}

exit_unlock:
- mutex_unlock(&switch_lock);
+ mutex_unlock(&sw->tb->lock);

if (ret)
return ret;
@@ -949,8 +942,8 @@ static ssize_t nvm_version_show(struct device *dev,
struct tb_switch *sw = tb_to_switch(dev);
int ret;

- if (mutex_lock_interruptible(&switch_lock))
- return -ERESTARTSYS;
+ if (!mutex_trylock(&sw->tb->lock))
+ return restart_syscall();

if (sw->safe_mode)
ret = -ENODATA;
@@ -959,7 +952,7 @@ static ssize_t nvm_version_show(struct device *dev,
else
ret = sprintf(buf, "%x.%x\n", sw->nvm->major, sw->nvm->minor);

- mutex_unlock(&switch_lock);
+ mutex_unlock(&sw->tb->lock);

return ret;
}
diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
index 496dcd03ede1..f7b0c43c29a7 100644
--- a/drivers/thunderbolt/tb.h
+++ b/drivers/thunderbolt/tb.h
@@ -79,8 +79,7 @@ struct tb_switch_nvm {
* @depth: Depth in the chain this switch is connected (ICM only)
*
* When the switch is being added or removed to the domain (other
- * switches) you need to have domain lock held. For switch authorization
- * internal switch_lock is enough.
+ * switches) you need to have domain lock held.
*/
struct tb_switch {
struct device dev;
--
2.20.1