Re: rcu: eqs related warnings in linux-next

[Frederic Weisbecker]

On Fri, Sep 28, 2012 at 02:51:03PM +0200, Sasha Levin wrote:
> Hi all,
> 
> While fuzzing with trinity inside a KVM tools guest with the latest linux-next kernel, I've stumbled on the following during boot:
> 
> [  199.224369] WARNING: at kernel/rcutree.c:513 rcu_eqs_exit_common+0x4a/0x3a0()
> [  199.225307] Pid: 1, comm: init Tainted: G        W    3.6.0-rc7-next-20120928-sasha-00001-g8b2d05d-dirty #13
> [  199.226611] Call Trace:
> [  199.226951]  [<ffffffff811c8d1a>] ? rcu_eqs_exit_common+0x4a/0x3a0
> [  199.227773]  [<ffffffff81108e36>] warn_slowpath_common+0x86/0xb0
> [  199.228572]  [<ffffffff81108f25>] warn_slowpath_null+0x15/0x20
> [  199.229348]  [<ffffffff811c8d1a>] rcu_eqs_exit_common+0x4a/0x3a0
> [  199.230037]  [<ffffffff8117f267>] ? __lock_acquire+0x1c37/0x1ca0
> [  199.230037]  [<ffffffff811c936c>] rcu_eqs_exit+0x9c/0xb0
> [  199.230037]  [<ffffffff811c940c>] rcu_user_exit+0x8c/0xf0
> [  199.230037]  [<ffffffff810a98bb>] do_page_fault+0x1b/0x40
> [  199.230037]  [<ffffffff810a2a90>] do_async_page_fault+0x30/0xa0
> [  199.230037]  [<ffffffff83a3eea8>] async_page_fault+0x28/0x30
> [  199.230037]  [<ffffffff819f357b>] ? debug_object_activate+0x6b/0x1b0
> [  199.230037]  [<ffffffff819f3586>] ? debug_object_activate+0x76/0x1b0
> [  199.230037]  [<ffffffff8111af13>] ? lock_timer_base.isra.19+0x33/0x70
> [  199.230037]  [<ffffffff8111d45f>] mod_timer_pinned+0x9f/0x260
> [  199.230037]  [<ffffffff811c5ff4>] rcu_eqs_enter_common+0x894/0x970
> [  199.230037]  [<ffffffff839dc2ac>] ? init_post+0x75/0xc8
> [  199.230037]  [<ffffffff85abfed5>] ? kernel_init+0x1e1/0x1e1
> [  199.230037]  [<ffffffff811c63df>] rcu_eqs_enter+0xaf/0xc0
> [  199.230037]  [<ffffffff811c64c5>] rcu_user_enter+0xd5/0x140
> [  199.230037]  [<ffffffff8107d0fd>] syscall_trace_leave+0xfd/0x150
> [  199.230037]  [<ffffffff83a3f7af>] int_check_syscall_exit_work+0x34/0x3d
> [  199.230037] ---[ end trace a582c3a264d5bd1a ]---

Ok, we can't decently protect against any kind of exception messing up everything
in the middle of RCU APIs anyway. The only solution is to find out what cause this
page fault in mod_timer_pinned() and work around that.

Anybody, an idea?
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