Messages in this thread | | | From | Vince Weaver <> | Date | Wed, 15 Oct 2014 14:34:10 -0400 (EDT) | Subject | Re: perf: 3.17 another perf_fuzzer lockup |
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OK, so it turns out that the oops I saw with memory corruption wasn't the bug I was tracking, but something that comes up sometimes when trying to run ftrace at the same time as fuzzing. So we'll leave that for another day.
The 3.17+ lockup I am tracking still reproduces as of git from yesterday (even after the 3.18-rc perf_event merges).
I can use sysrq to get the stack trace, the one CPU is stuck in a call to find_get_context().
An example backtrace:
[88200.300003] <EOI> [88200.300003] [<ffffffff81114869>] ? ____cache_alloc+0x130/0x25b [88200.300003] [<ffffffff8107fb05>] ? __call_rcu.constprop.63+0x1bf/0x1cb [88200.300003] [<ffffffff8107fb2b>] kfree_call_rcu+0x1a/0x1c [88200.300003] [<ffffffff810cf84f>] put_ctx+0x51/0x55 [88200.300003] [<ffffffff810d1840>] find_get_context+0x166/0x195 [88200.300003] [<ffffffff810d5856>] SYSC_perf_event_open+0x47b/0x7f5 [88200.300003] [<ffffffff810d5f55>] SyS_perf_event_open+0xe/0x10 [88200.300003] [<ffffffff815362d6>] system_call_fastpath+0x16/0x1b
It looks like the else if (task->perf_event_ctxp[ctxn]) err = -EAGAIN;
case is triggering non-stop in the retry path of find_get_context() and so the kernel gets stuck forever retrying.
I can drop some printks in if it will help debug. I've tried running ftrace, but for whatever reason if I enable ftrace the bug won't trigger.
Vince
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