Re: trinity finds ftrace/perf bug. Film at 11.

[Dave Jones]

On Thu, Sep 12, 2013 at 02:19:13PM -0400, Steven Rostedt wrote:
 > 
 > This is something that either Peter or Frederic need to look at.

I spent yesterday trying to bisect this, but kept running into other perf/ftrace traces,
which makes it pretty much impossible.

The current one I'm staring at is this from LIST_DEBUG..

list_del corruption. next->prev should be prev (ffff88000fb812b0), but was ffff88000fb812b0. (next=ffff88009df8b7b0).

The sharp eyed will notice that those first two addresses are actually the same.
So we matched the next->prev != prev test, but at the time we got to the printk that follows
in the WARN, the inverse was true. Smells like a race of some kind.

[ 2481.228418] Call Trace:
[ 2481.232705]  [<ffffffff8171f5dd>] dump_stack+0x54/0x74
[ 2481.237025]  [<ffffffff810540bd>] warn_slowpath_common+0x7d/0xa0
[ 2481.241357]  [<ffffffff8105412c>] warn_slowpath_fmt+0x4c/0x50
[ 2481.245637]  [<ffffffff810540e5>] ? warn_slowpath_fmt+0x5/0x50
[ 2481.249890]  [<ffffffff8132c222>] __list_del_entry+0x62/0xf0
[ 2481.254109]  [<ffffffff81143a88>] list_del_event+0xc8/0xe0
[ 2481.258310]  [<ffffffff81143b2b>] perf_remove_from_context+0x8b/0xf0
[ 2481.262497]  [<ffffffff81145444>] perf_event_release_kernel+0x54/0x90
[ 2481.266688]  [<ffffffff811464d3>] put_event+0x133/0x1c0
[ 2481.270866]  [<ffffffff811463d0>] ? put_event+0x30/0x1c0
[ 2481.275066]  [<ffffffff81146570>] perf_release+0x10/0x20
[ 2481.279277]  [<ffffffff811bf2ca>] __fput+0xfa/0x2e0
[ 2481.283488]  [<ffffffff811bf4fe>] ____fput+0xe/0x10
[ 2481.287713]  [<ffffffff8107c11c>] task_work_run+0xac/0xe0
[ 2481.291958]  [<ffffffff810559bc>] do_exit+0x2cc/0xcc0
[ 2481.296194]  [<ffffffff81732880>] ? ftrace_call+0x5/0x2f
[ 2481.300435]  [<ffffffff810577cc>] do_group_exit+0x4c/0xc0
[ 2481.304654]  [<ffffffff81057854>] SyS_exit_group+0x14/0x20
[ 2481.308857]  [<ffffffff81732e54>] tracesys+0xdd/0xe2
[ 2481.313051] ---[ end trace fa3e551eb20e0c0f ]---

	Dave

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