From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx145.postini.com [74.125.245.145]) by kanga.kvack.org (Postfix) with SMTP id 4C91E6B002C for ; Thu, 8 Mar 2012 16:56:46 -0500 (EST) Date: Thu, 8 Mar 2012 13:56:43 -0800 From: Andrew Morton Subject: Re: [patch] mm, hugetlb: add thread name and pid to SHM_HUGETLB mlock rlimit warning Message-Id: <20120308135643.225920ad.akpm@linux-foundation.org> In-Reply-To: References: <20120308120238.c4486547.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Dave Jones , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Thu, 8 Mar 2012 13:37:57 -0800 (PST) David Rientjes wrote: > On Thu, 8 Mar 2012, Andrew Morton wrote: > > > > --- a/fs/hugetlbfs/inode.c > > > +++ b/fs/hugetlbfs/inode.c > > > @@ -946,7 +946,11 @@ struct file *hugetlb_file_setup(const char *name, size_t size, > > > if (creat_flags == HUGETLB_SHMFS_INODE && !can_do_hugetlb_shm()) { > > > *user = current_user(); > > > if (user_shm_lock(size, *user)) { > > > - printk_once(KERN_WARNING "Using mlock ulimits for SHM_HUGETLB is deprecated\n"); > > > + task_lock(current); > > > + printk_once(KERN_WARNING > > > + "%s (%d): Using mlock ulimits for SHM_HUGETLB is deprecated\n", > > > + current->comm, current->pid); > > > + task_unlock(current); > > > > I assume the task_lock() is there to protect current->comm. > > Yup. > > > If so, it > > is unneeded - we're protecting against prctl(PR_SET_NAME), and > > PR_SET_NAME only operates on current, and we know this task isn't > > currently running PR_SET_NAME. > > > > If there's a way for another task to alter this task's ->comm then we > > _do_ need locking. But there isn't a way, I hope. > > > > I wish there wasn't as well, it would prevent a lot of the currently buggy > reads to current->comm and allow us to avoid so many otherwise pointless > task_lock()s. > > This protects against /proc/pid/comm, which is writable by threads in the > same thread group. Oh crap. > We have a get_task_comm() that does the task_lock() > internally but requires a TASK_COMM_LEN buffer in the calling code. It's > just easier for the calling code to the task_lock() itself for a tiny > little printk(). Well for a tiny little printk we could just omit the locking? The printk() won't oops and once in a million years one person will see a garbled comm[] string? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org