Re: [PATCH] kernel-shark: Add check for return of ksmodel_get_cpu_front()

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On 11.05.21 г. 16:40, Steven Rostedt wrote:
On Tue, 11 May 2021 16:25:35 +0300
Yordan Karadzhov <y.karadz@xxxxxxxxx> wrote:

You can reproduce this with:

     http://rostedt.org/private/trace-no-map.tar.bz2

What should I do to make it SEGFAULT?
Y.


diff --git a/src/KsPlotTools.cpp b/src/KsPlotTools.cpp
index 225dc34..abef5f8 100644
--- a/src/KsPlotTools.cpp
+++ b/src/KsPlotTools.cpp
@@ -1280,7 +1280,7 @@ void Graph::fillTaskGraph(int sd, int pid)
   						 false,
   						 _collectionPtr,
   						 &index);

I wonder why this fails? Is it because "pid" is negative? The fix below
is appropriate, however we should detect negative PIDs and abort
plotting much earlier.

I believe the issue is that we failed to map which host task goes with
which guest vCPUU, and just randomly picked one (or none).

I fixed trace-cmd to get the mappings when qemu is not found, and
KernelShark works fine on that case. This bug only appears when it can't
find the host thread that corresponds to the guest vCPU.

-- Steve




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