Re: [PATCH v2] test: Account for large stack-limit kernel parameter

On Thu, Oct 09, 2025 at 05:33:42PM -0400, [email protected] wrote:
> From: Eugene Loh <[email protected]>
> 
> In commit d0fdeec50 ("test: Fix some ustackdepth tests"), the test was
> tweaked to check that the full stack would be recovered if the kernel
> stack-limit parameter were increased from a default 127 to greater than
> about 190 frames.  But this does not work if the system already has
> reset the kernel parameter to a high value.
> 
> Change the test to deliberately try a "too small" and a "big enough"
> value -- again, ultimately restoring the original value.
> 
> Signed-off-by: Eugene Loh <[email protected]>

Reviewed-by: Kris Van Hees <[email protected]>

> ---
>  .../variables/bvar/tst.ustackdepth_big.sh     | 106 +++++++++++-------
>  1 file changed, 68 insertions(+), 38 deletions(-)
> 
> diff --git a/test/unittest/variables/bvar/tst.ustackdepth_big.sh b/test/unittest/variables/bvar/tst.ustackdepth_big.sh
> index 4ce53d929..aeef9982c 100755
> --- a/test/unittest/variables/bvar/tst.ustackdepth_big.sh
> +++ b/test/unittest/variables/bvar/tst.ustackdepth_big.sh
> @@ -23,52 +23,82 @@ cd $DIRNAME
>  
>  orig_maxstack=`sysctl -n kernel.perf_event_max_stack`
>  echo kernel.perf_event_max_stack was $orig_maxstack
> -trap "sysctl kernel.perf_event_max_stack=$orig_maxstack" QUIT EXIT
> -sysctl kernel.perf_event_max_stack=200
> +trap "sleep 2; sysctl kernel.perf_event_max_stack=$orig_maxstack" QUIT EXIT
>  
> -$dtrace $dt_flags -c $TRIGGER -qn '
> -profile-1
> -/pid == $target/
> -{
> -    printf("DEPTH %d\n", ustackdepth);
> -    printf("TRACE BEGIN\n");
> -    ustack(200);
> -    printf("TRACE END\n");
> -    exit(0);
> -}
> -ERROR
> -{
> -    exit(1);
> -}
> -' > D.out
> -if [ $? -ne 0 ]; then
> -    echo DTrace failure
> -    exit 1
> -fi
> +# set bounds on the full stack depth (which is ambiguous)
> +lo=188
> +hi=192
>  
> -sleep 2
> -sysctl kernel.perf_event_max_stack=$orig_maxstack
> +function do_dtrace() {
> +    # set the kernel parameter
> +    sysctl kernel.perf_event_max_stack=$stack_limit
>  
> -$POSTPROC D.out > awk.out
> -if [ $? -ne 0 ]; then
> -    echo post processing failure
> -    exit 1
> -fi
> +    # run dtrace
> +    $dtrace $dt_flags -c $TRIGGER -qn '
> +    profile-1
> +    /pid == $target/
> +    {
> +        printf("DEPTH %d\n", ustackdepth);
> +        printf("TRACE BEGIN\n");
> +        ustack(200);
> +        printf("TRACE END\n");
> +        exit(0);
> +    }
> +    ERROR
> +    {
> +        exit(1);
> +    }
> +    ' > D.out.$stack_limit
> +    if [ $? -ne 0 ]; then
> +        echo ERROR: DTrace failure with $stack_limit
> +        exit 1
> +    fi
>  
> -if echo "Stack depth OK" | diff -q - awk.out; then
> -    mydepth=`gawk '/DEPTH/ { print $2 }' D.out`
> -    if [ $mydepth -gt $orig_maxstack ]; then
> -        echo success depth $mydepth exceeded original limit $orig_maxstack
> -        exit 0
> -    else
> -        echo ERROR: $mydepth does not exceed original limit $orig_maxstack
> +    # check stackdepth consistency
> +    $POSTPROC D.out.$stack_limit > awk.out.$stack_limit
> +    if [ $? -ne 0 ]; then
> +        echo ERROR: post processing failure
> +        exit 1
> +    fi
> +    if ! grep -q "Stack depth OK" awk.out.$stack_limit; then
> +        echo ERROR: stack depth does not match stack
>          cat D.out
>          exit 1
>      fi
> -else
> -    echo "ERROR: stack depth does not match stack"
> -    cat D.out
> +
> +    # get actual stack depth
> +    mydepth=`gawk '/DEPTH/ { print $2 }' D.out.$stack_limit`
> +    echo with limit $stack_limit got stack depth $mydepth
> +
> +    # provide breathing room between dtrace and resetting kernel parameter
> +    sleep 2
> +}
> +
> +# try a stack limit that is too small
> +stack_limit=$(($lo / 2))
> +do_dtrace
> +echo "   " stack limit $stack_limit is too small for the entire stack
> +if [ $mydepth -ne $stack_limit ]; then
> +    echo ERROR: $mydepth does not match $stack_limit
>      exit 1
>  fi
> +echo "   " success:  actual depth matches limit
> +
> +# try a stack limit that is large enough
> +stack_limit=$(($hi + 20))
> +do_dtrace
> +echo "   " stack limit $stack_limit is large enough
> +if [ $mydepth -lt $lo ]; then
> +    echo ERROR: $mydepth is lower than low bound $lo
> +    exit 1
> +fi
> +if [ $mydepth -gt $hi ]; then
> +    echo ERROR: $mydepth is greater than high bound $hi
> +    exit 1
> +fi
> +echo "   " success:  actual depth captures full stack
> +
> +# restore the kernel parameter
> +sysctl kernel.perf_event_max_stack=$orig_maxstack
>  
>  exit 0
> -- 
> 2.47.3
>