From: "Américo Wang" <xiyou.wangcong@gmail.com>
To: John Stultz <john.stultz@linaro.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Ted Ts'o <tytso@mit.edu>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
David Rientjes <rientjes@google.com>,
Dave Hansen <dave@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org
Subject: Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm
Date: Thu, 12 May 2011 18:43:05 +0800 [thread overview]
Message-ID: <BANLkTikxcfGYAmKf5QEAwJjDLdo6_k6zaw@mail.gmail.com> (raw)
In-Reply-To: <1305147776.2883.1.camel@work-vm>
On Thu, May 12, 2011 at 5:02 AM, John Stultz <john.stultz@linaro.org> wrote:
> On Wed, 2011-05-11 at 17:33 +0800, Américo Wang wrote:
>> On Wed, May 11, 2011 at 8:23 AM, John Stultz <john.stultz@linaro.org> wrote:
>> > Acessing task->comm requires proper locking. However in the past
>> > access to current->comm could be done without locking. This
>> > is no longer the case, so all comm access needs to be done
>> > while holding the comm_lock.
>> >
>> > In my attempt to clean up unprotected comm access, I've noticed
>> > most comm access is done for printk output. To simpify correct
>> > locking in these cases, I've introduced a new %ptc format,
>> > which will safely print the corresponding task's comm.
>> >
>> > Example use:
>> > printk("%ptc: unaligned epc - sending SIGBUS.\n", current);
>> >
>>
>> Why do you hide current->comm behide printk?
>> How is this better than printk("%s: ....", task_comm(current)) ?
>
> So to properly access current->comm, you need to hold the task-lock (or
> with my new patch set, the comm_lock). Rather then adding locking to all
> the call sites that printk("%s ...", current->comm), I'm suggesting we
> add a new %ptc method which will handle the locking for you.
>
Sorry, I meant why not adding the locking into a wrapper function,
probably get_task_comm() and let the users to call it directly?
Why is %ptc better than
char comm[...];
get_task_comm(comm, current);
printk("%s: ....", comm);
?
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next prev parent reply other threads:[~2011-05-12 10:43 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-11 0:23 [RFC][PATCH 0/3] v2 Improve task->comm locking situation John Stultz
2011-05-11 0:23 ` [PATCH 1/3] comm: Introduce comm_lock seqlock to protect task->comm access John Stultz
2011-05-11 17:39 ` Andi Kleen
2011-05-12 22:00 ` David Rientjes
2011-05-11 0:23 ` [PATCH 2/3] printk: Add %ptc to safely print a task's comm John Stultz
2011-05-11 0:51 ` Joe Perches
2011-05-11 1:10 ` John Stultz
2011-05-11 1:16 ` john stultz
2011-05-11 1:20 ` Joe Perches
2011-05-12 22:12 ` David Rientjes
2011-05-12 22:29 ` Joe Perches
2011-05-13 21:56 ` David Rientjes
2011-05-12 22:10 ` David Rientjes
2011-05-11 9:33 ` Américo Wang
2011-05-11 21:02 ` John Stultz
2011-05-12 10:43 ` Américo Wang [this message]
2011-05-12 10:45 ` Américo Wang
2011-05-12 18:01 ` John Stultz
2011-05-11 17:36 ` Andi Kleen
2011-05-11 21:04 ` John Stultz
2011-05-11 0:23 ` [PATCH 3/3] comm: ext4: Protect task->comm access by using %ptc John Stultz
2011-05-12 22:14 ` David Rientjes
2011-05-12 22:29 ` John Stultz
2011-05-12 22:34 ` Andrew Morton
2011-05-12 23:02 [PATCH 0/3] v3 Improve task->comm locking situation John Stultz
2011-05-12 23:02 ` [PATCH 2/3] printk: Add %ptc to safely print a task's comm John Stultz
2011-05-16 21:19 [PATCH 0/3] v4 Improve task->comm locking situation John Stultz
2011-05-16 21:19 ` [PATCH 2/3] printk: Add %ptc to safely print a task's comm John Stultz
2011-05-16 21:54 ` Jiri Slaby
2011-05-16 23:10 ` John Stultz
2011-05-16 23:56 ` Joe Perches
2011-05-17 0:11 ` John Stultz
2011-05-17 7:21 ` Jiri Slaby
2011-05-18 0:32 ` KOSAKI Motohiro
2011-05-17 20:47 [PATCH 0/3] v5 Improve task->comm locking situation John Stultz
2011-05-17 20:47 ` [PATCH 2/3] printk: Add %ptc to safely print a task's comm John Stultz
2011-05-17 21:42 ` Jiri Slaby
2011-05-17 21:52 ` Joe Perches
2011-05-17 22:04 ` Jiri Slaby
2011-05-17 22:17 ` Joe Perches
2011-05-17 22:17 ` John Stultz
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