From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Galbraith Date: Fri, 31 Dec 2010 08:32:30 +0000 Subject: [PATCH] Re: [PATCH] sched, cgroup: Use exit hook to avoid Message-Id: <1293784350.6839.2.camel@marge.simson.net> List-Id: References: <1293106330.2170.618.camel@laptop> <1293107624.2170.642.camel@laptop> <1293128670.2170.748.camel@laptop> <1293132304.6798.6.camel@marge.simson.net> <1293132862.25981.22.camel@laptop> <1293187425.7138.2.camel@marge.simson.net> <1293188091.25981.200.camel@laptop> <1293192999.18035.4.camel@marge.simson.net> <1293206353.29444.205.camel@laptop> <20101229152522.GA23825@elte.hu> In-Reply-To: <20101229152522.GA23825@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Ingo Molnar Cc: Peter Zijlstra , Miklos Vajna , shenghui , kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org, Greg KH , Paul Turner , Yong Zhang , Li Zefan , Paul Menage , Balbir Singh , Srivatsa Vaddagiri On Wed, 2010-12-29 at 16:25 +0100, Ingo Molnar wrote: > I tried this patch, but it causes a boot crash: The below should fix it. sched: fix autogroup reference leak and cpu_cgroup_exit() explosion In the event of a fork failure, the new cpu_cgroup_exit() method tries to move an unhashed task. Since PF_EXITING isn't set in that case, autogroup will dig aground in a freed signal_struct. Neither cgroups nor autogroup has anything it needs to do with this shade, so don't go there. This also uncovered a struct autogroup reference leak. copy_process() was simply freeing vs putting the signal_struct, stranding a reference. Signed-off-by: Mike Galbraith --- kernel/fork.c | 2 +- kernel/sched.c | 10 ++++++++++ 2 files changed, 11 insertions(+), 1 deletion(-) Index: linux-2.6.37.git/kernel/fork.c =================================--- linux-2.6.37.git.orig/kernel/fork.c +++ linux-2.6.37.git/kernel/fork.c @@ -1318,7 +1318,7 @@ bad_fork_cleanup_mm: } bad_fork_cleanup_signal: if (!(clone_flags & CLONE_THREAD)) - free_signal_struct(p->signal); + put_signal_struct(p->signal); bad_fork_cleanup_sighand: __cleanup_sighand(p->sighand); bad_fork_cleanup_fs: Index: linux-2.6.37.git/kernel/sched.c =================================--- linux-2.6.37.git.orig/kernel/sched.c +++ linux-2.6.37.git/kernel/sched.c @@ -9193,6 +9193,16 @@ cpu_cgroup_attach(struct cgroup_subsys * static void cpu_cgroup_exit(struct cgroup_subsys *ss, struct task_struct *task) { + /* + * cgroup_exit() is called in the copy_process failure path. + * The task isn't hashed, and we don't want to make autogroup + * dig into a freed signal_struct, so just go away. + * + * XXX: why are cgroup methods diddling unattached tasks? + */ + if (!(task->flags & PF_EXITING)) + return; + sched_move_task(task); }