linux-kernel - Re: [Intel-gfx] [PATCH v4 02/10] lib/ref_tracker: __ref_tracker_dir

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Message-ID: <81ae464f-ade8-fb3c-6bfa-11de19c21845@intel.com>
Date:   Mon, 20 Mar 2023 16:39:01 +0100
From:   Andrzej Hajda <andrzej.hajda@...el.com>
To:     Andi Shyti <andi.shyti@...ux.intel.com>
Cc:     Chris Wilson <chris.p.wilson@...el.com>, netdev@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Eric Dumazet <edumazet@...gle.com>,
        dri-devel@...ts.freedesktop.org, Daniel Vetter <daniel@...ll.ch>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Airlie <airlied@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [Intel-gfx] [PATCH v4 02/10] lib/ref_tracker:
 __ref_tracker_dir_print improve printing

On 20.03.2023 00:11, Andi Shyti wrote:
> Hi Andrzej,
> 
> looks good, few comments below,
> 
> On Mon, Mar 06, 2023 at 05:31:58PM +0100, Andrzej Hajda wrote:
>> To improve readability of ref_tracker printing following changes
>> have been performed:
>> - reports are printed per stack_handle - log is more compact,
>> - added display name for ref_tracker_dir,
>> - stack trace is printed indented, in the same printk call,
>> - total number of references is printed every time,
>> - print info about dropped references.
> 
> nit: I think you can do better with the log :)
> 
>> Signed-off-by: Andrzej Hajda <andrzej.hajda@...el.com>
>> ---
>>   include/linux/ref_tracker.h | 15 ++++++--
>>   lib/ref_tracker.c           | 90 +++++++++++++++++++++++++++++++++++++++------
>>   2 files changed, 91 insertions(+), 14 deletions(-)
>>
>> diff --git a/include/linux/ref_tracker.h b/include/linux/ref_tracker.h
>> index 3e9e9df2a41f5f..a2cf1f6309adb2 100644
>> --- a/include/linux/ref_tracker.h
>> +++ b/include/linux/ref_tracker.h
>> @@ -17,12 +17,19 @@ struct ref_tracker_dir {
>>   	bool			dead;
>>   	struct list_head	list; /* List of active trackers */
>>   	struct list_head	quarantine; /* List of dead trackers */
>> +	char			name[32];
>>   #endif
>>   };
>>   
>>   #ifdef CONFIG_REF_TRACKER
>> -static inline void ref_tracker_dir_init(struct ref_tracker_dir *dir,
>> -					unsigned int quarantine_count)
>> +
>> +// Temporary allow two and three arguments, until consumers are converted
> 
> I thought only Linus was allowed to use '//' :)
> 
>> +#define ref_tracker_dir_init(_d, _q, args...) _ref_tracker_dir_init(_d, _q, ##args, #_d)
>> +#define _ref_tracker_dir_init(_d, _q, _n, ...) __ref_tracker_dir_init(_d, _q, _n)
> 
> [...]
> 
>> +void __ref_tracker_dir_print(struct ref_tracker_dir *dir,
>> +			   unsigned int display_limit)
>> +{
>> +	struct ref_tracker_dir_stats *stats;
>> +	unsigned int i = 0, skipped;
>> +	depot_stack_handle_t stack;
>> +	char *sbuf;
>> +
>> +	lockdep_assert_held(&dir->lock);
>> +
>> +	if (list_empty(&dir->list))
>> +		return;
>> +
>> +	stats = ref_tracker_get_stats(dir, display_limit);
>> +	if (IS_ERR(stats)) {
>> +		pr_err("%s@%pK: couldn't get stats, error %pe\n",
>> +		       dir->name, dir, stats);
>> +		return;
>>   	}
>> +
>> +	sbuf = kmalloc(STACK_BUF_SIZE, GFP_NOWAIT | __GFP_NOWARN);
>> +
>> +	for (i = 0, skipped = stats->total; i < stats->count; ++i) {
>> +		stack = stats->stacks[i].stack_handle;
>> +		if (sbuf && !stack_depot_snprint(stack, sbuf, STACK_BUF_SIZE, 4))
>> +			sbuf[0] = 0;
>> +		pr_err("%s@%pK has %d/%d users at\n%s\n", dir->name, dir,
>> +		       stats->stacks[i].count, stats->total, sbuf);
> 
> what if sbuf is NULL?

Then "(NULL)" will be printed, I suspect it will occur only on very rare 
occasions.

> 
>> +		skipped -= stats->stacks[i].count;
>> +	}
>> +
>> +	if (skipped)
> 
> is skipped used to double check whether stats->count is equal to
> all the stacks[].conunts? What are the cases when skipped is > 0?

There is display_limit parameter, so the function prints up to 
display_limit reports, and brief summary on remaining ones - the skipped 
ones.

Regards
Andrzej


> 
> Andi
> 
>> +		pr_err("%s@%pK skipped reports about %d/%d users.\n",
>> +		       dir->name, dir, skipped, stats->total);
>> +
>> +	kfree(sbuf);
>> +
>> +	kfree(stats);
>>   }
>>   EXPORT_SYMBOL(__ref_tracker_dir_print);
>>   
>>
>> -- 
>> 2.34.1