Date: Wed, 15 Feb 2012 22:32:03 +0400
From: Cyrill Gorcunov <gorcunov@openvz.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
        Pavel Emelyanov <xemul@parallels.com>,
        Andrey Vagin <avagin@openvz.org>,
        KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
        Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Glauber Costa <glommer@parallels.com>,
        Andi Kleen <andi@firstfloor.org>, Tejun Heo <tj@kernel.org>,
        Matt Helsley <matthltc@us.ibm.com>, Pekka Enberg <penberg@kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Vasiliy Kulikov <segoon@openwall.com>,
        Alexey Dobriyan <adobriyan@gmail.com>, Valdis.Kletnieks@vt.edu,
        Michal Marek <mmarek@suse.cz>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree
Message-ID: <20120215183203.GH4533@moon>
References: <20120215143606.GA14037@redhat.com>
 <20120215151008.GL1894@moon>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20120215151008.GL1894@moon>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1312
Lines: 51

On Wed, Feb 15, 2012 at 07:10:08PM +0400, Cyrill Gorcunov wrote:
> On Wed, Feb 15, 2012 at 03:36:06PM +0100, Oleg Nesterov wrote:
> > 
> > task->files can be NULL, we can race with exit_files().
> 
> So I need to call get_files_struct. Thanks Oleg!
> 

Something like below I think, right? (it seems this
patc doesn't hit lenux-next yet, so here is interdiff
output)

	Cyrill
---
diff -u linux-2.6.git/kernel/kcmp.c linux-2.6.git/kernel/kcmp.c
--- linux-2.6.git/kernel/kcmp.c
+++ linux-2.6.git/kernel/kcmp.c
@@ -44,16 +44,25 @@
 static struct file *
 get_file_raw_ptr(struct task_struct *task, unsigned int idx)
 {
+	struct files_struct *files;
 	struct fdtable *fdt;
 	struct file *file;
 
-	spin_lock(&task->files->file_lock);
-	fdt = files_fdtable(task->files);
+	files = get_files_struct(task);
+	if (!files)
+		return NULL;
+
+	rcu_read_lock();
+
+	fdt = files_fdtable(files);
 	if (idx < fdt->max_fds)
 		file = fdt->fd[idx];
 	else
 		file = NULL;
-	spin_unlock(&task->files->file_lock);
+
+	rcu_read_unlock();
+
+	put_files_struct(files);
 
 	return file;
 }
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/