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

On Apr 9, 2020, at 10:14 AM, Steven Rostedt [off-list ref] wrote:

On Thu, 9 Apr 2020 06:06:35 -0400
Qian Cai [off-list ref] wrote:

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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  

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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...

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8e99cf91b99b tracing: Do not allocate buffer in trace_find_next_entry() in atomic

Touches reading the trace buffer.

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2ab2a0924b99 tracing: Add documentation on set_ftrace_notrace_pid and set_event_notrace_pid

Documentation.

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6a13a0d7b4d1 ftrace/kprobe: Show the maxactive number on kprobe_events

kprobe output.

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c9b7a4a72ff6 ring-buffer/tracing: Have iterator acknowledge dropped events

Reading the buffer.

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06e0a548bad0 tracing: Do not disable tracing when reading the trace file

Reading the buffer.

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1039221cc278 ring-buffer: Do not disable recording when there is an iterator

Reading the buffer.

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07b8b10ec94f ring-buffer: Make resize disable per cpu buffer instead of total buffer

Resizing the buffer.

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153368ce1bd0 ring-buffer: Optimize rb_iter_head_event()

Reading the buffer.

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ff84c50cfb4b ring-buffer: Do not die if rb_iter_peek() fails more than thrice

Reading the buffer.

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785888c544e0 ring-buffer: Have rb_iter_head_event() handle concurrent writer

Reading the buffer.

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28e3fc56a471 ring-buffer: Add page_stamp to iterator for synchronization

Reading the buffer.

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bc1a72afdc4a ring-buffer: Rename ring_buffer_read() to read_buffer_iter_advance()

Reading the buffer.

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ead6ecfddea5 ring-buffer: Have ring_buffer_empty() not depend on tracing stopped

Reading the buffer.

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ff895103a84a tracing: Save off entry when peeking at next entry

Reading the buffer.

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bf2cbe044da2 tracing: Use address-of operator on section symbols

Affects trace_printk()

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bbd9d05618a6 gpu/trace: add a gpu total memory usage tracepoint

New tracepoint infrastructure (just new trace events for gpu)

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89b74cac7834 tools/bootconfig: Show line and column in parse error

Extended command line boot config.

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306b69dce926 bootconfig: Support O=<builddir> option

Extended command line boot config

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5412e0b763e0 tracing: Remove unused TRACE_BUFFER bits

Removed unused enums.

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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