From: Tejun Heo Subject: [PATCH 07/12] cgroup: cgroup->subsys[] should be cleared after the css is offlined Date: Thu, 27 Mar 2014 22:40:56 -0400 Message-ID: <1395974461-12735-8-git-send-email-tj@kernel.org> References: <1395974461-12735-1-git-send-email-tj@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:from:to:cc:subject:date:message-id:in-reply-to:references; bh=g6Tfuso2Fpp7SSzQ7Toqz7YXl3LepkG7OMZMDG3dWOA=; b=j2X0gCvqXZ+4amsxNM+gntKihMnU2wm9FCPcqihFCM9HALGhGsrU/G87VGOiWGdgJp 2RGCnJ2z1pVKENi9LYHSV6SYXNA2fdNXknGZO2YdBfq1xy/2scAa0pfAihAVhJKdgXTX RYWAFQNMipbtFT22OfJGJvY2kwZ7BLWuqPXtsU8L3DYwzxKrJbDEKYdemcsVWfddrfTh 5k1DbYFZGHOvtKV+LCaTIE+4jNDy0q9bmCz7NCZlBCRsJ0kkD5v3DeBA0ShmRLx6wPyj 57BpJu6Bls+/hK88QfSD7GvfgBF6S7dFhlvKK1Y1h0qFXV9gdep3AXE24UaoSBA/dT6Q fA5A== In-Reply-To: <1395974461-12735-1-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org Cc: Tejun Heo , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org After a css finishes offlining, offline_css() mistakenly performs RCU_INIT_POINTER(css->cgroup->subsys[ss->id], css) which just sets the cgroup->subsys[] pointer to the current value. The intention was to clear it after offline is complete, not reassign the same value. Update it to assign NULL instead of the current value. This makes cgroup_css() to return NULL once offline is complete. All the existing users of the function either can handle NULL return already or guarantee that the css doesn't get offlined. While this is a bugfix, as css lifetime is currently tied to the cgroup it belongs to, this bug doesn't cause any actual problems. Signed-off-by: Tejun Heo Acked-by: Li Zefan --- kernel/cgroup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index e3aa2aa..c59946c 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -3692,7 +3692,7 @@ static void offline_css(struct cgroup_subsys_state *css) css->flags &= ~CSS_ONLINE; css->cgroup->nr_css--; - RCU_INIT_POINTER(css->cgroup->subsys[ss->id], css); + RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL); } /** -- 1.8.5.3