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From: Yordan Karadzhov <y.karadz@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Linux Trace Devel <linux-trace-devel@vger.kernel.org>
Subject: Re: [PATCH] kernel-shark: Add check for return of ksmodel_get_cpu_front()
Date: Tue, 11 May 2021 16:25:35 +0300	[thread overview]
Message-ID: <2bc740d1-e093-17d1-a9ba-b4319e0ebbfa@gmail.com> (raw)
In-Reply-To: <20210507093848.72bf0bed@gandalf.local.home>

Hi Steven,

On 7.05.21 г. 16:38, Steven Rostedt wrote:
> From: Steven Rostedt (VMware) <rostedt@goodmis.org>
> 
> When I loaded two trace.dat files (host and guest), but the mapping of
> which host thread is associated to which guest vCPU was missing from the
> file, it caused a SEGFAULT. That's because in fillTaskGraph(), the
> lamGetPidCPU() calls ksmodule_get_cpu_front() which returns a negative
> number and does not set index. But the next line checks data[index] where
> index is some random number, and the application crashes.
> 
> By checking the return of ksmodule_get_cpu_front(), and if it is negative
> do not reference data[index] and just let eFront be nullptr, the
> application shows no mapping, but at least it does not crash.
> 
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> ---
> You can reproduce this with:
> 
>     http://rostedt.org/private/trace-no-map.tar.bz2
> 
> 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.

Thanks!
Yordan

> -		if (index >= 0)
> +		if (cpuFront >= 0 && index >= 0)
>   			eFront = _histoPtr->data[index];
>   
>   		cpuBack = ksmodel_get_cpu_back(_histoPtr, bin,
> 

  reply	other threads:[~2021-05-11 13:25 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-07 13:38 [PATCH] kernel-shark: Add check for return of ksmodel_get_cpu_front() Steven Rostedt
2021-05-11 13:25 ` Yordan Karadzhov [this message]
2021-05-11 13:40   ` Steven Rostedt
2021-05-11 13:51     ` Yordan Karadzhov
2021-05-14 11:50 ` Yordan Karadzhov

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