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From: Oleg Nesterov <oleg@redhat.com>
To: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	jovi.zhangwei@huawei.com, Jiri Olsa <jolsa@redhat.com>,
	Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Subject: Re: Re: [RFC PATCH V2] tracing: Check f_dentry before accessing event_file/call in inode->i_private
Date: Fri, 19 Jul 2013 15:33:27 +0200	[thread overview]
Message-ID: <20130719133327.GA21278@redhat.com> (raw)
In-Reply-To: <51E8CCC0.7030404@hitachi.com>

On 07/19, Masami Hiramatsu wrote:
>
> (2013/07/18 23:51), Oleg Nesterov wrote:
> > It removes trace_array_get/put from tracing_open_generic_file() and
> > tracing_release_generic_file(). This assumes that "call->flags++" is
> > enough, but it is not.
>
> No, it replaces trace_array_get/put with ftrace_event_file_get/put
> which calls trace_array_get/put inside.

Ah, I didn't notice your patch adds "file->tr->ref++" into
ftrace_event_file_get...

So I was wrong in any case, thanks for correcting me.

But,

> (Just one point, previous ftrace_event_file_get has a racy point
> when it does tr->ref++, it should be fixed.)

Not sure what do you mean, but unless I missed something again this
"tr->ref++" above still looks racy. instance_delete() checks tr->ref
first, then it takes event_mutex and removes/kfrees event_files.

But this doesn't really matter even if I am right, surely this can
be fixed. My only point, imho this is more complex than necessary.

In particular,

> > IOW, I believe that either .open() should do trace_array_get(), or
> > __trace_remove_event_dirs() needs another for-each-file loop which
> > checks file->call->flags & TRACE_EVENT_FL_REF_MASK.
>
> Agreed :)

Yes ;) and this makes the ref-counting even more complex, we use
different methods to avoid the races with rmdir and event_remove().

> > The same bugs which Steven's 1/4 tries to solve ;)
>
> OK, let me confirm that, would you mean we still need 2/4 - 4/4?

Yes, yes.

Oleg.


  reply	other threads:[~2013-07-19 13:38 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-07-04  3:33 [RFC][PATCH 0/4] tracing/kprobes/uprobes: Fix race between opening probe event files and deleting probe Steven Rostedt
2013-07-04  3:33 ` [RFC][PATCH 1/4] tracing: Add ref count to ftrace_event_call Steven Rostedt
2013-07-04  4:22   ` Masami Hiramatsu
2013-07-04 11:55     ` [RFC PATCH] tracing: Atomically get refcounts of event_call and trace_array Masami Hiramatsu
2013-07-04 12:12       ` Masami Hiramatsu
2013-07-04 12:23         ` Steven Rostedt
2013-07-05  0:32       ` Oleg Nesterov
2013-07-05  2:32         ` Masami Hiramatsu
2013-07-09  7:55         ` [RFC PATCH V2] tracing: Check f_dentry before accessing event_file/call in inode->i_private Masami Hiramatsu
2013-07-15 18:16           ` Oleg Nesterov
2013-07-17  2:10             ` Masami Hiramatsu
2013-07-17 14:51               ` Oleg Nesterov
2013-07-18  2:20                 ` Masami Hiramatsu
2013-07-18 14:51                   ` Oleg Nesterov
2013-07-19  5:21                     ` Masami Hiramatsu
2013-07-19 13:33                       ` Oleg Nesterov [this message]
2013-07-22  9:57                         ` Masami Hiramatsu
2013-07-22 17:04                           ` Oleg Nesterov
2013-07-23 21:04                             ` Oleg Nesterov
2013-07-04  3:33 ` [RFC][PATCH 2/4] tracing: trace_remove_event_call() should fail if call/file is in use Steven Rostedt
2013-07-04 12:48   ` Masami Hiramatsu
2013-07-04  3:33 ` [RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probe event files are open Steven Rostedt
2013-07-04 12:45   ` Masami Hiramatsu
2013-07-04 18:48     ` Oleg Nesterov
2013-07-05  2:53       ` Masami Hiramatsu
2013-07-05 17:26         ` Oleg Nesterov
2013-07-08  2:36           ` Masami Hiramatsu
2013-07-08 14:25             ` Oleg Nesterov
2013-07-09  8:01               ` [RFC PATCH] tracing/kprobe: Wait for disabling all running kprobe handlers Masami Hiramatsu
2013-07-09  8:07                 ` Peter Zijlstra
2013-07-09  8:20                   ` Masami Hiramatsu
2013-07-09  8:21                     ` Peter Zijlstra
2013-07-09  8:50                       ` Masami Hiramatsu
2013-07-09  9:35                       ` [RFC PATCH V2] " Masami Hiramatsu
2013-07-15 18:20                         ` Oleg Nesterov
2013-07-18 12:07                           ` Masami Hiramatsu
2013-07-18 14:35                             ` Steven Rostedt
2013-07-30  8:15   ` [RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probe event files are open Masami Hiramatsu
2013-07-31 19:49   ` Steven Rostedt
2013-07-31 20:40     ` Oleg Nesterov
2013-07-31 22:42       ` Steven Rostedt
2013-08-01  2:07         ` Steven Rostedt
2013-08-01  2:50           ` Steven Rostedt
2013-08-01  3:48             ` Masami Hiramatsu
2013-08-01 13:34             ` Oleg Nesterov
2013-08-01 13:49               ` Oleg Nesterov
2013-08-01 14:17               ` Steven Rostedt
2013-08-01 14:33                 ` Oleg Nesterov
2013-08-01 14:45                   ` Steven Rostedt
2013-08-01 14:46                     ` Oleg Nesterov
2013-08-02  4:57               ` Masami Hiramatsu
2013-08-01 13:10         ` Oleg Nesterov
2013-07-04  3:33 ` [RFC][PATCH 4/4] tracing/uprobes: " Steven Rostedt
2013-08-01  3:40   ` Steven Rostedt
2013-08-01 14:08   ` Oleg Nesterov
2013-08-01 14:25     ` Steven Rostedt
2013-07-04  4:00 ` [RFC][PATCH 0/4] tracing/kprobes/uprobes: Fix race between opening probe event files and deleting probe Masami Hiramatsu
2013-07-04  6:14   ` Masami Hiramatsu
2013-07-12 13:09 ` Masami Hiramatsu
2013-07-12 17:53   ` Oleg Nesterov
2013-07-15 18:01 ` Oleg Nesterov
2013-07-16 16:38   ` Oleg Nesterov
2013-07-16 19:10     ` Steven Rostedt
2013-07-16 19:22       ` Oleg Nesterov
2013-07-16 19:38         ` Steven Rostedt
2013-07-17 16:03           ` Steven Rostedt
2013-07-17 17:37             ` Oleg Nesterov

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