Messages in this thread Patch in this message | | | Date | Tue, 29 Apr 2008 10:18:26 -0700 | From | Greg KH <> | Subject | [13/37] cgroup: fix a race condition in manipulating tsk->cg_list |
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2.6.25-stable review patch. If anyone has any objections, please let us know.
------------------ From: Li Zefan <lizf@cn.fujitsu.com>
commit: 0e04388f0189fa1f6812a8e1cb6172136eada87e
When I ran a test program to fork mass processes and at the same time 'cat /cgroup/tasks', I got the following oops:
------------[ cut here ]------------ kernel BUG at lib/list_debug.c:72! invalid opcode: 0000 [#1] SMP Pid: 4178, comm: a.out Not tainted (2.6.25-rc9 #72) ... Call Trace: [<c044a5f9>] ? cgroup_exit+0x55/0x94 [<c0427acf>] ? do_exit+0x217/0x5ba [<c0427ed7>] ? do_group_exit+0.65/0x7c [<c0427efd>] ? sys_exit_group+0xf/0x11 [<c0404842>] ? syscall_call+0x7/0xb [<c05e0000>] ? init_cyrix+0x2fa/0x479 ... EIP: [<c04df671>] list_del+0x35/0x53 SS:ESP 0068:ebc7df4 ---[ end trace caffb7332252612b ]--- Fixing recursive fault but reboot is needed!
After digging into the code and debugging, I finlly found out a race situation:
do_exit() ->cgroup_exit() ->if (!list_empty(&tsk->cg_list)) list_del(&tsk->cg_list);
cgroup_iter_start() ->cgroup_enable_task_cg_list() ->list_add(&tsk->cg_list, ..);
In this case the list won't be deleted though the process has exited.
We got two bug reports in the past, which seem to be the same bug as this one: http://lkml.org/lkml/2008/3/5/332 http://lkml.org/lkml/2007/10/17/224
Actually sometimes I got oops on list_del, sometimes oops on list_add. And I can change my test program a bit to trigger other oops.
The patch has been tested both on x86_32 and x86_64.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Acked-by: Paul Menage <menage@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- kernel/cgroup.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
--- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1722,7 +1722,12 @@ void cgroup_enable_task_cg_lists(void) use_task_css_set_links = 1; do_each_thread(g, p) { task_lock(p); - if (list_empty(&p->cg_list)) + /* + * We should check if the process is exiting, otherwise + * it will race with cgroup_exit() in that the list + * entry won't be deleted though the process has exited. + */ + if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list)) list_add(&p->cg_list, &p->cgroups->tasks); task_unlock(p); } while_each_thread(g, p); --
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