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

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Date:	Thu, 3 Jul 2008 11:47:15 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Masami Hiramatsu <mhiramat@...hat.com>
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)

* Masami Hiramatsu (mhiramat@...hat.com) wrote:
> 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;
> 

Ah, right, I had


        if (e->single.func != __mark_empty_function)
                return -EBUSY;

in the markers to test this and did not replace this test.

Thanks,

Mathieu

> > +	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
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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