Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm

Jiri Slaby
2011-05-16T21:54:31Z

On 05/16/2011 11:19 PM, John Stultz wrote:
> Accessing 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 simplify correct
> locking in these cases, I've introduced a new %ptc format,
> which will print the corresponding task's comm.
>
> Example use:
> printk("%ptc: unaligned epc - sending SIGBUS.\n", current);
>
> CC: Ted Ts'o <tytso@mit.edu>
> CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> CC: David Rientjes <rientjes@google.com>
> CC: Dave Hansen <dave@linux.vnet.ibm.com>
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: linux-mm@kvack.org
> Signed-off-by: John Stultz <john.stultz@linaro.org>
> ---
> lib/vsprintf.c | 24 ++++++++++++++++++++++++
> 1 files changed, 24 insertions(+), 0 deletions(-)
>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index bc0ac6b..b7a9953 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -797,6 +797,23 @@ char *uuid_string(char *buf, char *end, const u8 *addr,
> return string(buf, end, uuid, spec);
> }
>
> +static noinline_for_stack

Actually, why noinline? Did your previous version have there some
TASK_COMM_LEN buffer or anything on stack which is not there anymore?

> +char *task_comm_string(char *buf, char *end, void *addr,
> + struct printf_spec spec, const char *fmt)
> +{
> + struct task_struct *tsk = addr;
> + char *ret;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&tsk->comm_lock, flags);
> + ret = string(buf, end, tsk->comm, spec);
> + spin_unlock_irqrestore(&tsk->comm_lock, flags);
> +
> + return ret;
> +}
> +
> +
> +
> int kptr_restrict = 1;
>
> /*

thanks,
--
js