Re: [PATCH 1/3 v3] kernel/fork.c: avoid division by zero

Ingo Molnar
2015-02-22T07:58:32Z

* Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:

> PAGE_SIZE is not guaranteed to be equal to or less than 8 times the
> THREAD_SIZE.
>
> E.g. architecture hexagon may have page size 1M and thread size 4096.
> This would lead to a division by zero in the calculation of max_threads.
>
> With 32-bit calculus there is no solution which delivers valid results
> for all possible combinations of the parameters.
> The code is only called once.
> Hence a 64-bit calculation can be used as solution.
>
> The calculation of max_threads is moved to a separate function.
> This allows future patches to use the same logic, e.g. when
> - max_threads is set by writing to /proc/sys/kernel/threads-max
> - when adding or removing memory.
>
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
> ---
> kernel/fork.c | 59 ++++++++++++++++++++++++++++++++++++++++++-----------------
> 1 file changed, 42 insertions(+), 17 deletions(-)

So it would be nice to split this patch into two parts:
first do a patch that splits out a version of
set_max_threads() that matches current behavior (including
the bug).

Then a second patch that fixes the bug.

This would make it much easier to review.

Thanks,

Ingo