single_open() interface requires that the whole output must
fit into a single buffer. This will lead to timeout when
system memory is not in a good situation.
This patch use seq_open() to show wakeup stats. This method
need only one page, so timeout will not be observed.
Signed-off-by: Ganesh Mahendran <[email protected]>
---
drivers/base/power/wakeup.c | 71 +++++++++++++++++++++++++++++++++++----------
1 file changed, 56 insertions(+), 15 deletions(-)
diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
index ea01621..c64609a 100644
--- a/drivers/base/power/wakeup.c
+++ b/drivers/base/power/wakeup.c
@@ -1029,32 +1029,73 @@ static int print_wakeup_source_stats(struct seq_file *m,
return 0;
}
+static void *wakeup_sources_stats_seq_start(struct seq_file *m,
+ loff_t *pos)
+{
+ struct wakeup_source *ws;
+ loff_t n = *pos;
+
+ if (n == 0) {
+ seq_puts(m, "name\t\tactive_count\tevent_count\twakeup_count\t"
+ "expire_count\tactive_since\ttotal_time\tmax_time\t"
+ "last_change\tprevent_suspend_time\n");
+ }
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
+ if (n-- > 0)
+ continue;
+ goto out;
+ }
+ ws = NULL;
+out:
+ return ws;
+}
+
+static void *wakeup_sources_stats_seq_next(struct seq_file *m,
+ void *v, loff_t *pos)
+{
+ struct wakeup_source *ws = v;
+ struct wakeup_source *next_ws = NULL;
+
+ ++(*pos);
+
+ list_for_each_entry_continue_rcu(ws, &wakeup_sources, entry) {
+ next_ws = ws;
+ break;
+ }
+
+ return next_ws;
+}
+
+static void wakeup_sources_stats_seq_stop(struct seq_file *m, void *v)
+{
+ rcu_read_unlock();
+}
+
/**
* wakeup_sources_stats_show - Print wakeup sources statistics information.
* @m: seq_file to print the statistics into.
*/
-static int wakeup_sources_stats_show(struct seq_file *m, void *unused)
+static int wakeup_sources_stats_seq_show(struct seq_file *m, void *v)
{
- struct wakeup_source *ws;
- int srcuidx;
+ struct wakeup_source *ws = v;
- seq_puts(m, "name\t\tactive_count\tevent_count\twakeup_count\t"
- "expire_count\tactive_since\ttotal_time\tmax_time\t"
- "last_change\tprevent_suspend_time\n");
-
- srcuidx = srcu_read_lock(&wakeup_srcu);
- list_for_each_entry_rcu(ws, &wakeup_sources, entry)
- print_wakeup_source_stats(m, ws);
- srcu_read_unlock(&wakeup_srcu, srcuidx);
-
- print_wakeup_source_stats(m, &deleted_ws);
+ print_wakeup_source_stats(m, ws);
return 0;
}
+static const struct seq_operations wakeup_sources_stats_seq_ops = {
+ .start = wakeup_sources_stats_seq_start,
+ .next = wakeup_sources_stats_seq_next,
+ .stop = wakeup_sources_stats_seq_stop,
+ .show = wakeup_sources_stats_seq_show,
+};
+
static int wakeup_sources_stats_open(struct inode *inode, struct file *file)
{
- return single_open(file, wakeup_sources_stats_show, NULL);
+ return seq_open(file, &wakeup_sources_stats_seq_ops);
}
static const struct file_operations wakeup_sources_stats_fops = {
@@ -1062,7 +1103,7 @@ static int wakeup_sources_stats_open(struct inode *inode, struct file *file)
.open = wakeup_sources_stats_open,
.read = seq_read,
.llseek = seq_lseek,
- .release = single_release,
+ .release = seq_release,
};
static int __init wakeup_sources_debugfs_init(void)
--
1.9.1
On Fri 2018-03-02 13:01:00, Ganesh Mahendran wrote:
> single_open() interface requires that the whole output must
> fit into a single buffer. This will lead to timeout when
> system memory is not in a good situation.
>
> This patch use seq_open() to show wakeup stats. This method
> need only one page, so timeout will not be observed.
Can the rcu_read_unlock be delayed arbitrarily by userland code?
Is that ok with RCU?
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
On Fri, Mar 2, 2018 at 10:05 AM, Pavel Machek <[email protected]> wrote:
> On Fri 2018-03-02 13:01:00, Ganesh Mahendran wrote:
>> single_open() interface requires that the whole output must
>> fit into a single buffer. This will lead to timeout when
>> system memory is not in a good situation.
>>
>> This patch use seq_open() to show wakeup stats. This method
>> need only one page, so timeout will not be observed.
>
> Can the rcu_read_unlock be delayed arbitrarily by userland code?
>
> Is that ok with RCU?
No, it isn't. :-)
On Fri, Mar 2, 2018 at 9:58 AM, Rafael J. Wysocki <[email protected]> wrote:
> On Fri, Mar 2, 2018 at 6:01 AM, Ganesh Mahendran
> <[email protected]> wrote:
>> single_open() interface requires that the whole output must
>> fit into a single buffer. This will lead to timeout when
>> system memory is not in a good situation.
>
> Did you actually see this problem with this particular file or is it
> theoretical?
>
>> This patch use seq_open() to show wakeup stats. This method
>> need only one page, so timeout will not be observed.
>>
>> Signed-off-by: Ganesh Mahendran <[email protected]>
>> ---
>> drivers/base/power/wakeup.c | 71 +++++++++++++++++++++++++++++++++++----------
>> 1 file changed, 56 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
>> index ea01621..c64609a 100644
>> --- a/drivers/base/power/wakeup.c
>> +++ b/drivers/base/power/wakeup.c
>> @@ -1029,32 +1029,73 @@ static int print_wakeup_source_stats(struct seq_file *m,
>> return 0;
>> }
>>
>> +static void *wakeup_sources_stats_seq_start(struct seq_file *m,
>> + loff_t *pos)
>> +{
>> + struct wakeup_source *ws;
>> + loff_t n = *pos;
>> +
>> + if (n == 0) {
>> + seq_puts(m, "name\t\tactive_count\tevent_count\twakeup_count\t"
>> + "expire_count\tactive_since\ttotal_time\tmax_time\t"
>> + "last_change\tprevent_suspend_time\n");
>> + }
>> +
>> + rcu_read_lock();
>
> The code running after this cannot sleep. Use
> srcu_read_lock(&wakeup_srcu) instead.
But generally, as Pavel points it out, even under srcu_read_lock()
things cannot be delayed indefinitely (at least for actions other than
freeing up more memory), so the entire approach appears to be flawed.
On Fri, Mar 2, 2018 at 6:01 AM, Ganesh Mahendran
<[email protected]> wrote:
> single_open() interface requires that the whole output must
> fit into a single buffer. This will lead to timeout when
> system memory is not in a good situation.
Did you actually see this problem with this particular file or is it
theoretical?
> This patch use seq_open() to show wakeup stats. This method
> need only one page, so timeout will not be observed.
>
> Signed-off-by: Ganesh Mahendran <[email protected]>
> ---
> drivers/base/power/wakeup.c | 71 +++++++++++++++++++++++++++++++++++----------
> 1 file changed, 56 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
> index ea01621..c64609a 100644
> --- a/drivers/base/power/wakeup.c
> +++ b/drivers/base/power/wakeup.c
> @@ -1029,32 +1029,73 @@ static int print_wakeup_source_stats(struct seq_file *m,
> return 0;
> }
>
> +static void *wakeup_sources_stats_seq_start(struct seq_file *m,
> + loff_t *pos)
> +{
> + struct wakeup_source *ws;
> + loff_t n = *pos;
> +
> + if (n == 0) {
> + seq_puts(m, "name\t\tactive_count\tevent_count\twakeup_count\t"
> + "expire_count\tactive_since\ttotal_time\tmax_time\t"
> + "last_change\tprevent_suspend_time\n");
> + }
> +
> + rcu_read_lock();
The code running after this cannot sleep. Use
srcu_read_lock(&wakeup_srcu) instead.
> + list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
> + if (n-- > 0)
> + continue;
> + goto out;
> + }
> + ws = NULL;
> +out:
> + return ws;
> +}
> +
> +static void *wakeup_sources_stats_seq_next(struct seq_file *m,
> + void *v, loff_t *pos)
> +{
> + struct wakeup_source *ws = v;
> + struct wakeup_source *next_ws = NULL;
> +
> + ++(*pos);
> +
> + list_for_each_entry_continue_rcu(ws, &wakeup_sources, entry) {
> + next_ws = ws;
> + break;
> + }
> +
> + return next_ws;
> +}
> +
> +static void wakeup_sources_stats_seq_stop(struct seq_file *m, void *v)
> +{
> + rcu_read_unlock();
> +}
> +
> /**
> * wakeup_sources_stats_show - Print wakeup sources statistics information.
> * @m: seq_file to print the statistics into.
> */
> -static int wakeup_sources_stats_show(struct seq_file *m, void *unused)
> +static int wakeup_sources_stats_seq_show(struct seq_file *m, void *v)
> {
> - struct wakeup_source *ws;
> - int srcuidx;
> + struct wakeup_source *ws = v;
>
> - seq_puts(m, "name\t\tactive_count\tevent_count\twakeup_count\t"
> - "expire_count\tactive_since\ttotal_time\tmax_time\t"
> - "last_change\tprevent_suspend_time\n");
> -
> - srcuidx = srcu_read_lock(&wakeup_srcu);
> - list_for_each_entry_rcu(ws, &wakeup_sources, entry)
> - print_wakeup_source_stats(m, ws);
> - srcu_read_unlock(&wakeup_srcu, srcuidx);
> -
> - print_wakeup_source_stats(m, &deleted_ws);
> + print_wakeup_source_stats(m, ws);
>
> return 0;
> }
>
> +static const struct seq_operations wakeup_sources_stats_seq_ops = {
> + .start = wakeup_sources_stats_seq_start,
> + .next = wakeup_sources_stats_seq_next,
> + .stop = wakeup_sources_stats_seq_stop,
> + .show = wakeup_sources_stats_seq_show,
> +};
> +
> static int wakeup_sources_stats_open(struct inode *inode, struct file *file)
> {
> - return single_open(file, wakeup_sources_stats_show, NULL);
> + return seq_open(file, &wakeup_sources_stats_seq_ops);
> }
>
> static const struct file_operations wakeup_sources_stats_fops = {
> @@ -1062,7 +1103,7 @@ static int wakeup_sources_stats_open(struct inode *inode, struct file *file)
> .open = wakeup_sources_stats_open,
> .read = seq_read,
> .llseek = seq_lseek,
> - .release = single_release,
> + .release = seq_release,
> };
>
> static int __init wakeup_sources_debugfs_init(void)
> --
> 1.9.1
>
Hi, Rafael:
2018-03-02 16:58 GMT+08:00 Rafael J. Wysocki <[email protected]>:
> On Fri, Mar 2, 2018 at 6:01 AM, Ganesh Mahendran
> <[email protected]> wrote:
>> single_open() interface requires that the whole output must
>> fit into a single buffer. This will lead to timeout when
>> system memory is not in a good situation.
>
> Did you actually see this problem with this particular file or is it
> theoretical?
We got report of android watchdog timeout when memory situation
is bad.
>
>> This patch use seq_open() to show wakeup stats. This method
>> need only one page, so timeout will not be observed.
>>
>> Signed-off-by: Ganesh Mahendran <[email protected]>
>> ---
>> drivers/base/power/wakeup.c | 71 +++++++++++++++++++++++++++++++++++----------
>> 1 file changed, 56 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
>> index ea01621..c64609a 100644
>> --- a/drivers/base/power/wakeup.c
>> +++ b/drivers/base/power/wakeup.c
>> @@ -1029,32 +1029,73 @@ static int print_wakeup_source_stats(struct seq_file *m,
>> return 0;
>> }
>>
>> +static void *wakeup_sources_stats_seq_start(struct seq_file *m,
>> + loff_t *pos)
>> +{
>> + struct wakeup_source *ws;
>> + loff_t n = *pos;
>> +
>> + if (n == 0) {
>> + seq_puts(m, "name\t\tactive_count\tevent_count\twakeup_count\t"
>> + "expire_count\tactive_since\ttotal_time\tmax_time\t"
>> + "last_change\tprevent_suspend_time\n");
>> + }
>> +
>> + rcu_read_lock();
>
> The code running after this cannot sleep. Use
> srcu_read_lock(&wakeup_srcu) instead.
wakeup_sources_stats_seq_[start | end] are called in seq_read().
So rcu_read_unlock() will soon be called in seq_read().
I am not familar with rcu. I refered to kmemleak.c which use seq_open()
to show the stats.
Thanks for your review.
>
>> + list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
>> + if (n-- > 0)
>> + continue;
>> + goto out;
>> + }
>> + ws = NULL;
>> +out:
>> + return ws;
>> +}
>> +
>> +static void *wakeup_sources_stats_seq_next(struct seq_file *m,
>> + void *v, loff_t *pos)
>> +{
>> + struct wakeup_source *ws = v;
>> + struct wakeup_source *next_ws = NULL;
>> +
>> + ++(*pos);
>> +
>> + list_for_each_entry_continue_rcu(ws, &wakeup_sources, entry) {
>> + next_ws = ws;
>> + break;
>> + }
>> +
>> + return next_ws;
>> +}
>> +
>> +static void wakeup_sources_stats_seq_stop(struct seq_file *m, void *v)
>> +{
>> + rcu_read_unlock();
>> +}
>> +
>> /**
>> * wakeup_sources_stats_show - Print wakeup sources statistics information.
>> * @m: seq_file to print the statistics into.
>> */
>> -static int wakeup_sources_stats_show(struct seq_file *m, void *unused)
>> +static int wakeup_sources_stats_seq_show(struct seq_file *m, void *v)
>> {
>> - struct wakeup_source *ws;
>> - int srcuidx;
>> + struct wakeup_source *ws = v;
>>
>> - seq_puts(m, "name\t\tactive_count\tevent_count\twakeup_count\t"
>> - "expire_count\tactive_since\ttotal_time\tmax_time\t"
>> - "last_change\tprevent_suspend_time\n");
>> -
>> - srcuidx = srcu_read_lock(&wakeup_srcu);
>> - list_for_each_entry_rcu(ws, &wakeup_sources, entry)
>> - print_wakeup_source_stats(m, ws);
>> - srcu_read_unlock(&wakeup_srcu, srcuidx);
>> -
>> - print_wakeup_source_stats(m, &deleted_ws);
>> + print_wakeup_source_stats(m, ws);
>>
>> return 0;
>> }
>>
>> +static const struct seq_operations wakeup_sources_stats_seq_ops = {
>> + .start = wakeup_sources_stats_seq_start,
>> + .next = wakeup_sources_stats_seq_next,
>> + .stop = wakeup_sources_stats_seq_stop,
>> + .show = wakeup_sources_stats_seq_show,
>> +};
>> +
>> static int wakeup_sources_stats_open(struct inode *inode, struct file *file)
>> {
>> - return single_open(file, wakeup_sources_stats_show, NULL);
>> + return seq_open(file, &wakeup_sources_stats_seq_ops);
>> }
>>
>> static const struct file_operations wakeup_sources_stats_fops = {
>> @@ -1062,7 +1103,7 @@ static int wakeup_sources_stats_open(struct inode *inode, struct file *file)
>> .open = wakeup_sources_stats_open,
>> .read = seq_read,
>> .llseek = seq_lseek,
>> - .release = single_release,
>> + .release = seq_release,
>> };
>>
>> static int __init wakeup_sources_debugfs_init(void)
>> --
>> 1.9.1
>>
On Fri, Mar 2, 2018 at 12:34 PM, Ganesh Mahendran
<[email protected]> wrote:
> Hi, Rafael:
>
> 2018-03-02 16:58 GMT+08:00 Rafael J. Wysocki <[email protected]>:
>> On Fri, Mar 2, 2018 at 6:01 AM, Ganesh Mahendran
>> <[email protected]> wrote:
>>> single_open() interface requires that the whole output must
>>> fit into a single buffer. This will lead to timeout when
>>> system memory is not in a good situation.
>>
>> Did you actually see this problem with this particular file or is it
>> theoretical?
>
> We got report of android watchdog timeout when memory situation
> is bad.
I see.
>>
>>> This patch use seq_open() to show wakeup stats. This method
>>> need only one page, so timeout will not be observed.
>>>
>>> Signed-off-by: Ganesh Mahendran <[email protected]>
>>> ---
>>> drivers/base/power/wakeup.c | 71 +++++++++++++++++++++++++++++++++++----------
>>> 1 file changed, 56 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
>>> index ea01621..c64609a 100644
>>> --- a/drivers/base/power/wakeup.c
>>> +++ b/drivers/base/power/wakeup.c
>>> @@ -1029,32 +1029,73 @@ static int print_wakeup_source_stats(struct seq_file *m,
>>> return 0;
>>> }
>>>
>>> +static void *wakeup_sources_stats_seq_start(struct seq_file *m,
>>> + loff_t *pos)
>>> +{
>>> + struct wakeup_source *ws;
>>> + loff_t n = *pos;
>>> +
>>> + if (n == 0) {
>>> + seq_puts(m, "name\t\tactive_count\tevent_count\twakeup_count\t"
>>> + "expire_count\tactive_since\ttotal_time\tmax_time\t"
>>> + "last_change\tprevent_suspend_time\n");
>>> + }
>>> +
>>> + rcu_read_lock();
>>
>> The code running after this cannot sleep. Use
>> srcu_read_lock(&wakeup_srcu) instead.
>
> wakeup_sources_stats_seq_[start | end] are called in seq_read().
> So rcu_read_unlock() will soon be called in seq_read().
But you have to guarantee that the code between rcu_read_lock() and
rcu_read_unlock() will *never* sleep.
> I am not familar with rcu.
So you need to get familiar with it to make changes involving it.
Otherwise you may fall a victim of the Wizard's Second Rule.
> I refered to kmemleak.c which use seq_open()
> to show the stats.
I see.
You need to use srcu_read_lock(&wakeup_srcu) in this file anyway.