linux-kernel - Re: [RFC PATCH] Kernel Tracepoints (update)

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Message-ID: <486CEFDB.7070508@redhat.com>
Date:	Thu, 03 Jul 2008 11:27:23 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Takashi Nishiie <t-nishiie@...css.fujitsu.com>,
	"'Alexey Dobriyan'" <adobriyan@...il.com>,
	"'Peter Zijlstra'" <peterz@...radead.org>,
	"'Steven Rostedt'" <rostedt@...dmis.org>,
	"'Frank Ch. Eigler'" <fche@...hat.com>,
	"'Ingo Molnar'" <mingo@...e.hu>,
	"'LKML'" <linux-kernel@...r.kernel.org>,
	"'systemtap-ml'" <systemtap@...rces.redhat.com>,
	"'Hideo AOKI'" <haoki@...hat.com>
Subject: Re: [RFC PATCH] Kernel Tracepoints (update)

Hi Mathieu,

I found a bug.
Mathieu Desnoyers wrote:
[...]

> +/*
> + * Remove the tracepoint from the tracepoint hash table. Must be called with
> + * mutex_lock held.
> + */
> +static int remove_tracepoint(const char *name)
> +{
> +	struct hlist_head *head;
> +	struct hlist_node *node;
> +	struct tracepoint_entry *e;
> +	int found = 0;
> +	size_t len = strlen(name) + 1;
> +	u32 hash = jhash(name, len-1, 0);
> +
> +	head = &tracepoint_table[hash & ((1 << TRACEPOINT_HASH_BITS)-1)];
> +	hlist_for_each_entry(e, node, head, hlist) {
> +		if (!strcmp(name, e->name)) {
> +			found = 1;
> +			break;
> +		}
> +	}
> +	if (!found)
> +		return -ENOENT;

before removing, you have to ensure refcount == 0. So,
	if (e->refcount != 0)
		return -EBUSY;

> +	hlist_del(&e->hlist);
> +	/* Make sure the call_rcu has been executed */
> +	if (e->rcu_pending)
> +		rcu_barrier();
> +	kfree(e);
> +	return 0;
> +}

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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