linux-kernel - Re: Linux-next POWER9 NULL pointer NIP since 1st Apr.

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Message-Id: <06A2EA93-B730-4DB1-819F-D27E7032F0B3@lca.pw>
Date:   Fri, 10 Apr 2020 15:20:49 -0400
From:   Qian Cai <cai@....pw>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Linux-next POWER9 NULL pointer NIP since 1st Apr.



> On Apr 9, 2020, at 10:14 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> On Thu, 9 Apr 2020 06:06:35 -0400
> Qian Cai <cai@....pw> wrote:
> 
>>>> I’ll go to bisect some more but it is going to take a while.
>>>> 
>>>> $ git log --oneline 4c205c84e249..8e99cf91b99b
>>>> 8e99cf91b99b tracing: Do not allocate buffer in trace_find_next_entry() in atomic
>>>> 2ab2a0924b99 tracing: Add documentation on set_ftrace_notrace_pid and set_event_notrace_pid
>>>> ebed9628f5c2 selftests/ftrace: Add test to test new set_event_notrace_pid file
>>>> ed8839e072b8 selftests/ftrace: Add test to test new set_ftrace_notrace_pid file
>>>> 276836260301 tracing: Create set_event_notrace_pid to not trace tasks  
>>> 
>>>> b3b1e6ededa4 ftrace: Create set_ftrace_notrace_pid to not trace tasks
>>>> 717e3f5ebc82 ftrace: Make function trace pid filtering a bit more exact  
>>> 
>>> If it is affecting function tracing, it is probably one of the above two
>>> commits.  
>> 
>> OK, it was narrowed down to one of those messed with mcount here,
> 
> Thing is, nothing here touches mcount.

Yes, you are right. I went back to test the commit just before the 5.7-trace merge request,
I did reproduce there. The thing is that this bastard could take more 6-hour to happen,
so my previous attempt did not wait long enough. Back to the square one...

> 
>> 
>> 8e99cf91b99b tracing: Do not allocate buffer in trace_find_next_entry() in atomic
> 
> Touches reading the trace buffer.
> 
>> 2ab2a0924b99 tracing: Add documentation on set_ftrace_notrace_pid and set_event_notrace_pid
> 
> Documentation.
> 
>> 6a13a0d7b4d1 ftrace/kprobe: Show the maxactive number on kprobe_events
> 
> kprobe output.
> 
>> c9b7a4a72ff6 ring-buffer/tracing: Have iterator acknowledge dropped events
> 
> Reading the buffer.
> 
>> 06e0a548bad0 tracing: Do not disable tracing when reading the trace file
> 
> Reading the buffer.
> 
>> 1039221cc278 ring-buffer: Do not disable recording when there is an iterator
> 
> Reading the buffer.
> 
>> 07b8b10ec94f ring-buffer: Make resize disable per cpu buffer instead of total buffer
> 
> Resizing the buffer.
> 
>> 153368ce1bd0 ring-buffer: Optimize rb_iter_head_event()
> 
> Reading the buffer.
> 
>> ff84c50cfb4b ring-buffer: Do not die if rb_iter_peek() fails more than thrice
> 
> Reading the buffer.
> 
>> 785888c544e0 ring-buffer: Have rb_iter_head_event() handle concurrent writer
> 
> Reading the buffer.
> 
>> 28e3fc56a471 ring-buffer: Add page_stamp to iterator for synchronization
> 
> Reading the buffer.
> 
>> bc1a72afdc4a ring-buffer: Rename ring_buffer_read() to read_buffer_iter_advance()
> 
> Reading the buffer.
> 
>> ead6ecfddea5 ring-buffer: Have ring_buffer_empty() not depend on tracing stopped
> 
> Reading the buffer.
> 
>> ff895103a84a tracing: Save off entry when peeking at next entry
> 
> Reading the buffer.
> 
>> bf2cbe044da2 tracing: Use address-of operator on section symbols
> 
> Affects trace_printk()
> 
>> bbd9d05618a6 gpu/trace: add a gpu total memory usage tracepoint
> 
> New tracepoint infrastructure (just new trace events for gpu)
> 
>> 89b74cac7834 tools/bootconfig: Show line and column in parse error
> 
> Extended command line boot config.
> 
>> 306b69dce926 bootconfig: Support O=<builddir> option
> 
> Extended command line boot config
> 
>> 5412e0b763e0 tracing: Remove unused TRACE_BUFFER bits
> 
> Removed unused enums.
> 
>> b396bfdebffc tracing: Have hwlat ts be first instance and record count of instances
> 
> Affects only the hard ware latency detector (most likely not even
> configured in the kernel).
> 
> So I don't understand how any of the above commits can cause a problem.
> 
> -- Steve