Re: [PATCH] gdb: Fix instability in thread groups test

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2018-08-10 05:57, Andrew Burgess wrote:
> In the test script gdb.mi/list-thread-groups-available.exp we ask GDB
> to list all thread groups, and match the output against a
> regexp. Occasionally, I would see this test fail.
> 
> The expected output is a list of entries, each entry looking roughly
> like this:
> 
>   {id="<DECIMAL>",type="process",description="<STRING>",
>    user="<STRING>",cores=["<DECIMAL>","<DECIMAL>",...]}
> 
> All the fields after 'id' and 'type' are optional, and the 'cores'
> list can contain 1 or more "<DECIMAL>" entries.
> 
> On my machine (Running Fedora 27, kernel 4.17.3-100.fc27.x86_64)
> usually the 'description' is a non-empty string, and the 'cores' list
> has at least one entry in it.  But sometimes, very rarely, I'll see an
> entry in the process group list where the 'description' is an empty
> string, the 'user' is the string "?", and the 'cores' list is empty.
> Such an entry looks like this:
> 
>    {id="19863",type="process",description="",user="?",cores=[]}
> 
> I believe that this is caused by the process exiting while GDB is
> scanning /proc for process information.  The current code in
> gdb/nat/linux-osdata.c is not (I think) resilient against exiting
> processes.
> 
> This commit adjusts the regex that matches the 'cores' list so that an
> empty list is acceptable, with this patch in place the test script
> gdb.mi/list-thread-groups-available.exp never fails for me now.
> 
> gdb/testsuite/ChangeLog:
> 
> 	* gdb.mi/list-thread-groups-available.exp: Update test regexp.
> ---
>  gdb/testsuite/ChangeLog                               | 4 ++++
>  gdb/testsuite/gdb.mi/list-thread-groups-available.exp | 2 +-
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/testsuite/gdb.mi/list-thread-groups-available.exp
> b/gdb/testsuite/gdb.mi/list-thread-groups-available.exp
> index c4dab2a2c34..88f9ee9b63d 100644
> --- a/gdb/testsuite/gdb.mi/list-thread-groups-available.exp
> +++ b/gdb/testsuite/gdb.mi/list-thread-groups-available.exp
> @@ -45,7 +45,7 @@ set id_re "id=\"$decimal\""
>  set type_re "type=\"process\""
>  set description_re "description=\"$string_re\""
>  set user_re "user=\"$string_re\""
> -set cores_re "cores=\\\[\"$decimal\"(,\"$decimal\")*\\\]"
> +set cores_re "cores=\\\[(\"$decimal\"(,\"$decimal\")*)?\\\]"
> 
>  # List all available processes.
>  set process_entry_re
> "{${id_re},${type_re}(,$description_re)?(,$user_re)?(,$cores_re)?}"

Hi Andrew,

The patch LGTM.  I manually reproduced this case by spawning a process 
(tail -f /dev/null) and noting its pid.  In linux_xfer_osdata_processes, 
I added:

   if (pid == <pid>)
     sleep (5);

and killing the process during that sleep.

Simon