Hi, Rafael:
2018-03-02 16:58 GMT+08:00 Rafael J. Wysocki <raf...@kernel.org>:
> On Fri, Mar 2, 2018 at 6:01 AM, Ganesh Mahendran
> <opensource.gan...@gmail.com> 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 <opensource.gan...@gmail.com>
>> ---
>> 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
>>
