From: Frederic Weisbecker <fweisbec@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Li Zefan <lizf@cn.fujitsu.com>, Theodore Ts'o <tytso@mit.edu>,
LKML <linux-kernel@vger.kernel.org>,
linux-ext4@vger.kernel.org,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [BUG] ext4 trace events cause NULL pointer dereferences
Date: Wed, 21 Jul 2010 16:21:16 +0200 [thread overview]
Message-ID: <20100721142112.GB5764@nowhere> (raw)
In-Reply-To: <1279721766.4818.39.camel@gandalf.stny.rr.com>
On Wed, Jul 21, 2010 at 10:16:06AM -0400, Steven Rostedt wrote:
> On Wed, 2010-07-21 at 22:31 +0900, KOSAKI Motohiro wrote:
> > Hi Steven,
>
> > if (ac)
> > trace_ext4_mb_release_group_pa(ac, pa);
> >
> > But, I don't think this is proper fix because we don't want any overhead
> > if the tracepoint is disabled.
> >
> > So, How do we check NULL in TP_fast_assign()?
>
> You could do:
>
> TP_fast_assign(
> if (ac) {
> __entry->dev = ac->ac_sb->s_dev;
> __entry->ino = ac->ac_inode->i_ino;
> __entry->pa_pstart = pa->pa_pstart;
> __entry->pa_len = pa->pa_len;
> }
> ),
>
> But this just makes the __entry null and wastes the ring buffer.
>
> I may be able to add a __discard_entry that may help. Then we could do
> something like this:
>
> if (ac) {
> __entry->dev = ac->ac_sb->s_dev;
> __entry->ino = ac->ac_inode->i_ino;
> __entry->pa_pstart = pa->pa_pstart;
> __entry->pa_len = pa->pa_len;
> } else
> __discard_entry;
>
> Does this seem reasonable?
>
> But for now, the wasting the entry seems to be the only choice we have,
> or to do as you suggested and have the "if (ac) trace_...", but I don't
> like that.
>
> -- Steve
Is there no already existing branch in ext4 you could reuse in order to
send the trace only if (ac) ?
next prev parent reply other threads:[~2010-07-21 14:21 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-07-16 8:48 [BUG] ext4 trace events cause NULL pointer dereferences Li Zefan
2010-07-21 13:31 ` KOSAKI Motohiro
2010-07-21 14:16 ` Steven Rostedt
2010-07-21 14:21 ` Frederic Weisbecker [this message]
2010-07-22 5:45 ` Li Zefan
2010-07-22 5:49 ` Christoph Hellwig
2010-07-23 1:13 ` Ted Ts'o
2010-07-23 5:47 ` KOSAKI Motohiro
2010-07-23 9:11 ` Theodore Tso
2010-07-23 9:19 ` Li Zefan
2010-07-26 2:20 ` Li Zefan
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