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Date: Thu, 31 Jan 2013 07:50:10 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: chenggang.qin@gmail.com
Cc: linux-kernel@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@redhat.com>, David Ahern <dsahern@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Paul Mackerras <paulus@samba.org>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Namhyung Kim <namhyung@gmail.com>,
        Yanmin Zhang <yanmin.zhang@intel.com>,
        Wu Fengguang <fengguang.wu@intel.com>, Mike Galbraith <efault@gmx.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Chenggang Qin <chenggang.qcg@alibaba-inc.com>
Subject: Re: [PATCH v3] Add 4 tracepoint events for vfs
Message-ID: <20130131075010.GM4503@ZenIV.linux.org.uk>
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On Thu, Jan 31, 2013 at 03:40:38PM +0800, chenggang.qin@gmail.com wrote:
> @@ -1391,12 +1394,16 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
>  	unsigned long seg = 0;
>  	size_t count;
>  	loff_t *ppos = &iocb->ki_pos;
> +	const unsigned char *f_name;
>  
>  	count = 0;
>  	retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
>  	if (retval)
>  		return retval;
>  
> +	f_name = filp->f_path.dentry->d_name.name;
> +	trace_generic_file_aio_read(pos, iov_length(iov, nr_segs), f_name);

And just what is going to prevent that f_name of yours from being freed
just as you are passing it to the function you are calling?

IOW, NAK.  BTW, I would like to point out that *ANY* hooks in VFS have all
the stability granted to driver API - removal fodder whenever it becomes
convenient.