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Date:   Thu, 9 Apr 2020 10:14:13 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Qian Cai <cai@lca.pw>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
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Subject: Re: Linux-next POWER9 NULL pointer NIP since 1st Apr.
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On Thu, 9 Apr 2020 06:06:35 -0400
Qian Cai <cai@lca.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.

> 
> 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