linux-kernel - Re: [RFC][PATCH 0/4] tracing/kprobes/uprobes: Fix race between opening probe event files and deleting probe

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Date:	Tue, 16 Jul 2013 18:38:04 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH 0/4] tracing/kprobes/uprobes: Fix race between
	opening probe event files and deleting probe

On 07/15, Oleg Nesterov wrote:
>
> So. As Masami pointed out, this is not enough. Probably we can add more
> hacks, but I'd like to discuss the alternative approach.
>
> Note also that this ref count has the unfortunate property, if someone
> keeps the file opened we can't remove an event.

And please correct me, but afaics there are similar problems with
rmdir instances/xxx.

> What this patch does:
>
> 	- add the new "topmost" rw_semaphore, file_sem.

probably unneeded...

> 	- trace_remove_event_call() takes this sem for writing and
> 	  cleares enable/id/format/filter->i_private
>
> 	- removes tracing_open_generic_file/tracing_release_generic_file,
> 	  we do not use file->f_private any longer
>
> 	- changes event_enable_read/event_enable_write to read
> 	  ftrace_event_file = i_private under read_lock(file_sem) and
> 	  abort if it is null.
>
> Question: why event_enable_write() needs trace_array_get() ?

probably it doesn't...

> Steven, Masami, do you think this can make any sense?

Oleg.

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