Re: [PATCH] mm/kasan/kasan.h: Fix boolean checking issue for kasan_report_enabled()

[Alexander Potapenko <glider@google.com>]

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Don't bother, I'll refactor {en,dis}able_current().

sent from phone
On May 14, 2016 5:30 AM, "Chen Gang" <chengang@emindsoft.com.cn> wrote:

> Hello all:
>
> Shall I send patch v2 for it? (if really need, please let me know, and I
> shall try).
>
> Default, I shall continue to try to find and send another patches for mm
> in "include/linux/*.h".
>
> Thanks.
>
> On 5/3/16 00:38, Chen Gang wrote:
> > On 5/3/16 00:23, Chen Gang wrote:
> >> On 5/2/16 23:35, Alexander Potapenko wrote:
> >>> On Mon, May 2, 2016 at 5:13 PM, Chen Gang <chengang@emindsoft.com.cn>
> wrote:
> >>>>
> >>>> OK. But it does not look quite easy to use kasan_disable_current() for
> >>>> INIT_KASAN which is used in INIT_TASK.
> >>>>
> >>>> If we have to set "kasan_depth == 1", we have to use kasan_depth-- in
> >>>> kasan_enable_current().
> >>> Agreed, decrementing the counter in kasan_enable_current() is more
> natural.
> >>> I can fix this together with the comments.
> >>
> >> OK, thanks. And need I also send patch v2 for include/linux/kasan.h? (or
> >> you will fix them together).
> >>
> >>>>
> >>>> If we don't prevent the overflow, it will have negative effect with
> the
> >>>> caller. When we issue an warning, it means the caller's hope fail, but
> >>>> can not destroy the caller's original work. In our case:
> >>>>
> >>>>  - Assume "kasan_depth-- for kasan_enable_current()", the first enable
> >>>>    will let kasan_depth be 0.
> >>> Sorry, I'm not sure I follow.
> >>> If we start with kasan_depth=0 (which is the default case for every
> >>> task except for the init, which also gets kasan_depth=0 short after
> >>> the kernel starts),
> >>> then the first call to kasan_disable_current() will make kasan_depth
> >>> nonzero and will disable KASAN.
> >>> The subsequent call to kasan_enable_current() will enable KASAN back.
> >>>
> >>> There indeed is a problem when someone calls kasan_enable_current()
> >>> without previously calling kasan_disable_current().
> >>> In this case we need to check that kasan_depth was zero and print a
> >>> warning if it was.
> >>> It actually does not matter whether we modify kasan_depth after that
> >>> warning or not, because we are already in inconsistent state.
> >>> But I think we should modify kasan_depth anyway to ease the debugging.
> >>>
> >
> > Oh, sorry, I forgot one of our original discussing content:
> >
> >  - If we use signed int kasan_depth, and kasan_depth <= 0 means enable, I
> >    guess, we can always modify kasan_depth.
> >
> >  - When overflow/underflow (singed int overflow), we can use BUG_ON(),
> >    since it should be rarely happen.
> >
> > Thanks.
> >
> >>
> >> For me, BUG_ON() will be better for debugging, but it is really not well
> >> for using.  For WARN_ON(), it already print warnings, so I am not quite
> >> sure "always modifying kasan_depth will be ease the debugging".
> >>
> >> When we are in inconsistent state, for me, what we can do is:
> >>
> >>  - Still try to do correct things within our control: "when the caller
> >>    make a mistake, if kasan_enable_current() notices about it, it need
> >>    issue warning, and prevent itself to make mistake (causing disable).
> >>
> >>  - "try to let negative effect smaller to user", e.g. let users "loose
> >>    hope" (call enable has no effect) instead of destroying users'
> >>    original work (call enable, but get disable).
> >>
> >> Thanks.
> >>
> >
>
> --
> Chen Gang (陈刚)
>
> Managing Natural Environments is the Duty of Human Beings.
>

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