linux-kernel - Re: [PATCH v3 5/7] tracing: Add 'hist' event trigger command

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Message-ID: <CAADnVQJfw7HOCjitz9jQX+VDQj7QjwSsCH0pP+JfoGUHpvetOQ@mail.gmail.com>
Date:	Sat, 4 Apr 2015 08:36:44 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 5/7] tracing: Add 'hist' event trigger command

On Fri, Apr 3, 2015 at 8:51 AM, Tom Zanussi <tom.zanussi@...ux.intel.com> wrote:
> +static struct hist_trigger_entry *
> +tracing_map_insert(struct tracing_map *map, void *key)
> +{
> +       u32 idx, key_hash, test_key;
> +
> +       key_hash = jhash(key, map->key_size, 0);
> +       idx = key_hash >> (32 - (map->map_bits + 1));
> +
> +       while (1) {
> +               idx &= (map->map_size - 1);
> +               test_key = map->map[idx].key;
> +
> +               if (test_key && test_key == key_hash &&
> +                   keys_match(key, map->map[idx].val->key, map->key_size))
> +                       return map->map[idx].val;
> +
> +               if (!test_key && !cmpxchg(&map->map[idx].key, 0, key_hash)) {
> +                       struct hist_trigger_entry *entry;
> +
> +                       entry = hist_trigger_entry_create(map);
> +                       if (!entry)
> +                               break;
> +                       memcpy(entry->key, key, map->key_size);
> +                       map->map[idx].val = entry;
> +
> +                       return map->map[idx].val;
> +               }

There is obvious race here, since algorithm is not implemented correctly.
Partially inserted key/value is not handled.
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