It's not obvious how the code prevents adding more than 31 elements to
the list and thus invoking undefined behaviour in the 1 << new_lbid
expression, and in practice causing ->lbid values to repeat every 32
elements.
But the definition of struct gb_loopback is local to loopback.c, and the
lbid field is entirely unused outside of this function, so it seems we
can just drop it entirely.
Signed-off-by: Rasmus Villemoes <[email protected]>
---
Since lbid isn't mentioned anywhere else in greybus/, it's hard to
figure out how it was meant to be used. It does seem like entirely
dead (write-only) code.
drivers/staging/greybus/loopback.c | 8 --------
1 file changed, 8 deletions(-)
diff --git a/drivers/staging/greybus/loopback.c b/drivers/staging/greybus/loopback.c
index 42f6f3de967c..7080294f705c 100644
--- a/drivers/staging/greybus/loopback.c
+++ b/drivers/staging/greybus/loopback.c
@@ -97,7 +97,6 @@ struct gb_loopback {
u32 timeout_min;
u32 timeout_max;
u32 outstanding_operations_max;
- u32 lbid;
u64 elapsed_nsecs;
u32 apbridge_latency_ts;
u32 gbphy_latency_ts;
@@ -1014,16 +1013,9 @@ static int gb_loopback_bus_id_compare(void *priv, struct list_head *lha,
static void gb_loopback_insert_id(struct gb_loopback *gb)
{
- struct gb_loopback *gb_list;
- u32 new_lbid = 0;
-
/* perform an insertion sort */
list_add_tail(&gb->entry, &gb_dev.list);
list_sort(NULL, &gb_dev.list, gb_loopback_bus_id_compare);
- list_for_each_entry(gb_list, &gb_dev.list, entry) {
- gb_list->lbid = 1 << new_lbid;
- new_lbid++;
- }
}
#define DEBUGFS_NAMELEN 32
--
2.19.0
gb_loopback_bus_id_compare only has a single caller, and it no longer
needs to have a prototype compatible with being a callback for
list_sort.
Signed-off-by: Rasmus Villemoes <[email protected]>
---
drivers/staging/greybus/loopback.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/drivers/staging/greybus/loopback.c b/drivers/staging/greybus/loopback.c
index 89c3f6fd8ddf..2c7bad66bb31 100644
--- a/drivers/staging/greybus/loopback.c
+++ b/drivers/staging/greybus/loopback.c
@@ -987,11 +987,8 @@ static const struct file_operations gb_loopback_debugfs_latency_ops = {
.release = single_release,
};
-static int gb_loopback_bus_id_compare(void *priv, struct list_head *lha,
- struct list_head *lhb)
+static int gb_loopback_bus_id_compare(struct gb_loopback *a, struct gb_loopback *b)
{
- struct gb_loopback *a = list_entry(lha, struct gb_loopback, entry);
- struct gb_loopback *b = list_entry(lhb, struct gb_loopback, entry);
struct gb_connection *ca = a->connection;
struct gb_connection *cb = b->connection;
@@ -1022,7 +1019,7 @@ static void gb_loopback_insert_id(struct gb_loopback *gb)
* and we thus insert at the end.
*/
list_for_each_entry(gb_list, &gb_dev.list, entry) {
- if (gb_loopback_bus_id_compare(NULL, &gb->entry, &gb_list->entry) < 0)
+ if (gb_loopback_bus_id_compare(gb, gb_list) < 0)
break;
}
list_add_tail(&gb->entry, &gb_list->entry);
--
2.19.0
"Append to the list and do a merge sort" is not really an insertion
sort. While a few more lines of code, we can keep the list sorted doing
at most n comparisons by iterating until we find the first element
strictly greater than gb.
Signed-off-by: Rasmus Villemoes <[email protected]>
---
I have no idea if the performance matters (it probably doesn't). Feel
free to ignore this and the followup cleanup.
drivers/staging/greybus/loopback.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/drivers/staging/greybus/loopback.c b/drivers/staging/greybus/loopback.c
index 7080294f705c..89c3f6fd8ddf 100644
--- a/drivers/staging/greybus/loopback.c
+++ b/drivers/staging/greybus/loopback.c
@@ -1013,9 +1013,19 @@ static int gb_loopback_bus_id_compare(void *priv, struct list_head *lha,
static void gb_loopback_insert_id(struct gb_loopback *gb)
{
- /* perform an insertion sort */
- list_add_tail(&gb->entry, &gb_dev.list);
- list_sort(NULL, &gb_dev.list, gb_loopback_bus_id_compare);
+ struct gb_loopback *gb_list;
+
+ /*
+ * Keep the list sorted. Insert gb before the first element it
+ * compares strictly less than. If no such element exists, the
+ * loop terminates with &gb_list->entry being &gb_dev.list,
+ * and we thus insert at the end.
+ */
+ list_for_each_entry(gb_list, &gb_dev.list, entry) {
+ if (gb_loopback_bus_id_compare(NULL, &gb->entry, &gb_list->entry) < 0)
+ break;
+ }
+ list_add_tail(&gb->entry, &gb_list->entry);
}
#define DEBUGFS_NAMELEN 32
--
2.19.0
On 05/10/2018 15:28, Rasmus Villemoes wrote:
> Since lbid isn't mentioned anywhere else in greybus/, it's hard to
> figure out how it was meant to be used. It does seem like entirely
> dead (write-only) code.
>
yep, dead code
Reviewed-by: Bryan O'Donoghue <[email protected]>
On 05/10/2018 15:28, Rasmus Villemoes wrote:
> Signed-off-by: Rasmus Villemoes<[email protected]>
> ---
> I have no idea if the performance matters (it probably doesn't). Feel
> free to ignore this and the followup cleanup.
What's the problem you're fixing here ?
Is it tested ?
On 2018-10-11 01:03, Bryan O'Donoghue wrote:
> On 05/10/2018 15:28, Rasmus Villemoes wrote:
>> Signed-off-by: Rasmus Villemoes<[email protected]>
>> ---
>> I have no idea if the performance matters (it probably doesn't). Feel
>> free to ignore this and the followup cleanup.
>
> What's the problem you're fixing here ?
No problem, really, other than my inner Paul Hogan telling me "That's
not an insertion sort, ...".
> Is it tested ?
Compile-tested. As I said, if the performance (and inaccurate comment)
is irrelevant, just drop it.
Rasmus
On 2018-10-11 01:03, Bryan O'Donoghue wrote:
> On 05/10/2018 15:28, Rasmus Villemoes wrote:
>> Signed-off-by: Rasmus Villemoes<[email protected]>
>> ---
>> I have no idea if the performance matters (it probably doesn't). Feel
>> free to ignore this and the followup cleanup.
>
> What's the problem you're fixing here ?
>
> Is it tested ?
I got curious why one would want to keep a linked list sorted in the
first place (it can't be for doing binary searches). But it seems that
gb_loopback_device::list is unused, along with the list_op_async. Given
that the below compiles, doesn't that prove that the code is
dead/unused, or what am I missing?
diff --git a/drivers/staging/greybus/loopback.c
b/drivers/staging/greybus/loopback.c
index 7080294f705c..e4d42c1dc284 100644
--- a/drivers/staging/greybus/loopback.c
+++ b/drivers/staging/greybus/loopback.c
@@ -47,8 +47,6 @@ struct gb_loopback_device {
/* We need to take a lock in atomic context */
spinlock_t lock;
- struct list_head list;
- struct list_head list_op_async;
wait_queue_head_t wq;
};
@@ -68,7 +66,6 @@ struct gb_loopback {
struct kfifo kfifo_lat;
struct mutex mutex;
struct task_struct *task;
- struct list_head entry;
struct device *dev;
wait_queue_head_t wq;
wait_queue_head_t wq_completion;
@@ -987,37 +984,6 @@ static const struct file_operations
gb_loopback_debugfs_latency_ops = {
.release = single_release,
};
-static int gb_loopback_bus_id_compare(void *priv, struct list_head *lha,
- struct list_head *lhb)
-{
- struct gb_loopback *a = list_entry(lha, struct gb_loopback, entry);
- struct gb_loopback *b = list_entry(lhb, struct gb_loopback, entry);
- struct gb_connection *ca = a->connection;
- struct gb_connection *cb = b->connection;
-
- if (ca->bundle->intf->interface_id < cb->bundle->intf->interface_id)
- return -1;
- if (cb->bundle->intf->interface_id < ca->bundle->intf->interface_id)
- return 1;
- if (ca->bundle->id < cb->bundle->id)
- return -1;
- if (cb->bundle->id < ca->bundle->id)
- return 1;
- if (ca->intf_cport_id < cb->intf_cport_id)
- return -1;
- else if (cb->intf_cport_id < ca->intf_cport_id)
- return 1;
-
- return 0;
-}
-
-static void gb_loopback_insert_id(struct gb_loopback *gb)
-{
- /* perform an insertion sort */
- list_add_tail(&gb->entry, &gb_dev.list);
- list_sort(NULL, &gb_dev.list, gb_loopback_bus_id_compare);
-}
-
#define DEBUGFS_NAMELEN 32
static int gb_loopback_probe(struct gb_bundle *bundle,
@@ -1113,7 +1079,6 @@ static int gb_loopback_probe(struct gb_bundle *bundle,
}
spin_lock_irqsave(&gb_dev.lock, flags);
- gb_loopback_insert_id(gb);
gb_dev.count++;
spin_unlock_irqrestore(&gb_dev.lock, flags);
@@ -1169,7 +1134,6 @@ static void gb_loopback_disconnect(struct
gb_bundle *bundle)
spin_lock_irqsave(&gb_dev.lock, flags);
gb_dev.count--;
- list_del(&gb->entry);
spin_unlock_irqrestore(&gb_dev.lock, flags);
device_unregister(gb->dev);
@@ -1196,8 +1160,6 @@ static int loopback_init(void)
{
int retval;
- INIT_LIST_HEAD(&gb_dev.list);
- INIT_LIST_HEAD(&gb_dev.list_op_async);
spin_lock_init(&gb_dev.lock);
gb_dev.root = debugfs_create_dir("gb_loopback", NULL);
On 23/10/2018 17:20, Rasmus Villemoes wrote:
> On 2018-10-11 01:03, Bryan O'Donoghue wrote:
>> On 05/10/2018 15:28, Rasmus Villemoes wrote:
>>> Signed-off-by: Rasmus Villemoes<[email protected]>
>>> ---
>>> I have no idea if the performance matters (it probably doesn't). Feel
>>> free to ignore this and the followup cleanup.
>>
>> What's the problem you're fixing here ?
>>
>> Is it tested ?
>
> I got curious why one would want to keep a linked list sorted in the
> first place (it can't be for doing binary searches). But it seems that
> gb_loopback_device::list is unused, along with the list_op_async. Given
> that the below compiles, doesn't that prove that the code is
> dead/unused, or what am I missing?
>
> diff --git a/drivers/staging/greybus/loopback.c
> b/drivers/staging/greybus/loopback.c
> index 7080294f705c..e4d42c1dc284 100644
> --- a/drivers/staging/greybus/loopback.c
> +++ b/drivers/staging/greybus/loopback.c
> @@ -47,8 +47,6 @@ struct gb_loopback_device {
>
> /* We need to take a lock in atomic context */
> spinlock_t lock;
> - struct list_head list;
> - struct list_head list_op_async;
> wait_queue_head_t wq;
> };
>
> @@ -68,7 +66,6 @@ struct gb_loopback {
> struct kfifo kfifo_lat;
> struct mutex mutex;
> struct task_struct *task;
> - struct list_head entry;
> struct device *dev;
> wait_queue_head_t wq;
> wait_queue_head_t wq_completion;
> @@ -987,37 +984,6 @@ static const struct file_operations
> gb_loopback_debugfs_latency_ops = {
> .release = single_release,
> };
>
> -static int gb_loopback_bus_id_compare(void *priv, struct list_head *lha,
> - struct list_head *lhb)
> -{
> - struct gb_loopback *a = list_entry(lha, struct gb_loopback, entry);
> - struct gb_loopback *b = list_entry(lhb, struct gb_loopback, entry);
> - struct gb_connection *ca = a->connection;
> - struct gb_connection *cb = b->connection;
> -
> - if (ca->bundle->intf->interface_id < cb->bundle->intf->interface_id)
> - return -1;
> - if (cb->bundle->intf->interface_id < ca->bundle->intf->interface_id)
> - return 1;
> - if (ca->bundle->id < cb->bundle->id)
> - return -1;
> - if (cb->bundle->id < ca->bundle->id)
> - return 1;
> - if (ca->intf_cport_id < cb->intf_cport_id)
> - return -1;
> - else if (cb->intf_cport_id < ca->intf_cport_id)
> - return 1;
> -
> - return 0;
> -}
> -
> -static void gb_loopback_insert_id(struct gb_loopback *gb)
> -{
> - /* perform an insertion sort */
> - list_add_tail(&gb->entry, &gb_dev.list);
> - list_sort(NULL, &gb_dev.list, gb_loopback_bus_id_compare);
> -}
> -
> #define DEBUGFS_NAMELEN 32
>
> static int gb_loopback_probe(struct gb_bundle *bundle,
> @@ -1113,7 +1079,6 @@ static int gb_loopback_probe(struct gb_bundle *bundle,
> }
>
> spin_lock_irqsave(&gb_dev.lock, flags);
> - gb_loopback_insert_id(gb);
> gb_dev.count++;
> spin_unlock_irqrestore(&gb_dev.lock, flags);
>
> @@ -1169,7 +1134,6 @@ static void gb_loopback_disconnect(struct
> gb_bundle *bundle)
>
> spin_lock_irqsave(&gb_dev.lock, flags);
> gb_dev.count--;
> - list_del(&gb->entry);
> spin_unlock_irqrestore(&gb_dev.lock, flags);
>
> device_unregister(gb->dev);
> @@ -1196,8 +1160,6 @@ static int loopback_init(void)
> {
> int retval;
>
> - INIT_LIST_HEAD(&gb_dev.list);
> - INIT_LIST_HEAD(&gb_dev.list_op_async);
> spin_lock_init(&gb_dev.lock);
> gb_dev.root = debugfs_create_dir("gb_loopback", NULL);
>
Looks like dead code alright.
Reviewed-by: Bryan O'Donoghue <[email protected]>
gb_loopback_device::list_op_async is never used except for the
LIST_INIT. The ::list field appears to have a few more uses, but on
closer inspection the linked list of struct gb_loopbacks that it heads
is never used for anything, so there's no reason to maintain it, much
less to keep it sorted.
Reviewed-by: Bryan O'Donoghue <[email protected]>
Signed-off-by: Rasmus Villemoes <[email protected]>
---
Sending as a proper patch. Marked v2 since this replaces earlier 2/3
and 3/3 patches. Applies on top of
b4fc4e8340784e000030c5a59bf0791f9c3ce15e (staging: greybus:
loopback.c: remove unused gb_loopback::lbid).
drivers/staging/greybus/loopback.c | 38 ------------------------------
1 file changed, 38 deletions(-)
diff --git a/drivers/staging/greybus/loopback.c b/drivers/staging/greybus/loopback.c
index 7080294f705c..e4d42c1dc284 100644
--- a/drivers/staging/greybus/loopback.c
+++ b/drivers/staging/greybus/loopback.c
@@ -47,8 +47,6 @@ struct gb_loopback_device {
/* We need to take a lock in atomic context */
spinlock_t lock;
- struct list_head list;
- struct list_head list_op_async;
wait_queue_head_t wq;
};
@@ -68,7 +66,6 @@ struct gb_loopback {
struct kfifo kfifo_lat;
struct mutex mutex;
struct task_struct *task;
- struct list_head entry;
struct device *dev;
wait_queue_head_t wq;
wait_queue_head_t wq_completion;
@@ -987,37 +984,6 @@ static const struct file_operations gb_loopback_debugfs_latency_ops = {
.release = single_release,
};
-static int gb_loopback_bus_id_compare(void *priv, struct list_head *lha,
- struct list_head *lhb)
-{
- struct gb_loopback *a = list_entry(lha, struct gb_loopback, entry);
- struct gb_loopback *b = list_entry(lhb, struct gb_loopback, entry);
- struct gb_connection *ca = a->connection;
- struct gb_connection *cb = b->connection;
-
- if (ca->bundle->intf->interface_id < cb->bundle->intf->interface_id)
- return -1;
- if (cb->bundle->intf->interface_id < ca->bundle->intf->interface_id)
- return 1;
- if (ca->bundle->id < cb->bundle->id)
- return -1;
- if (cb->bundle->id < ca->bundle->id)
- return 1;
- if (ca->intf_cport_id < cb->intf_cport_id)
- return -1;
- else if (cb->intf_cport_id < ca->intf_cport_id)
- return 1;
-
- return 0;
-}
-
-static void gb_loopback_insert_id(struct gb_loopback *gb)
-{
- /* perform an insertion sort */
- list_add_tail(&gb->entry, &gb_dev.list);
- list_sort(NULL, &gb_dev.list, gb_loopback_bus_id_compare);
-}
-
#define DEBUGFS_NAMELEN 32
static int gb_loopback_probe(struct gb_bundle *bundle,
@@ -1113,7 +1079,6 @@ static int gb_loopback_probe(struct gb_bundle *bundle,
}
spin_lock_irqsave(&gb_dev.lock, flags);
- gb_loopback_insert_id(gb);
gb_dev.count++;
spin_unlock_irqrestore(&gb_dev.lock, flags);
@@ -1169,7 +1134,6 @@ static void gb_loopback_disconnect(struct gb_bundle *bundle)
spin_lock_irqsave(&gb_dev.lock, flags);
gb_dev.count--;
- list_del(&gb->entry);
spin_unlock_irqrestore(&gb_dev.lock, flags);
device_unregister(gb->dev);
@@ -1196,8 +1160,6 @@ static int loopback_init(void)
{
int retval;
- INIT_LIST_HEAD(&gb_dev.list);
- INIT_LIST_HEAD(&gb_dev.list_op_async);
spin_lock_init(&gb_dev.lock);
gb_dev.root = debugfs_create_dir("gb_loopback", NULL);
--
2.19.1.6.gbde171bbf5