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Groups > linux.kernel > #1495681
| From | Linus Torvalds <torvalds@linux-foundation.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: BUG_ON() in workingset_node_shadows_dec() triggers |
| Date | 2016-10-05 05:30 +0200 |
| Message-ID | <soL45-3sX-3@gated-at.bofh.it> (permalink) |
| References | <sopdf-5Kn-3@gated-at.bofh.it> <soKrn-2ZC-1@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Tue, Oct 4, 2016 at 7:43 PM, Paul Gortmaker
<paul.gortmaker@windriver.com> wrote:
>
> A couple years ago Ingo had an idea to kill BUG_ON abuse that I made
> a 1st pass at. Back then it seemed nobody cared. Maybe that has since
> changed?
>
> https://lkml.org/lkml/2014/4/30/359
So we actually have the checkpatch warning already:
# avoid BUG() or BUG_ON()
if ($line =~ /\b(?:BUG|BUG_ON)\b/) {
my $msg_type = \&WARN;
$msg_type = \&CHK if ($file);
&{$msg_type}("AVOID_BUG",
"Avoid crashing the kernel - try
using WARN_ON & recovery code rather than BUG() or BUG_ON()\n" .
$herecurr);
}
but it doesn't trigger on VM_BUG_ON().
And I'm not convinced about replacing things with BUG_ON_AND_HALT(),
it simply doesn't fix the existing issue we have: people use BUG_ON(),
and worse, _when_ they use BUG_ON(), they use it instead of error
handling, so the code _around_ the BUG_ON() tends to then very much
depend on what the BUG_ON() checks.
This is actually one way that VM_BUG_ON() is better: it's very much by
design something that can be compiled away, so at least hopefully
nobody thinks of it as a security measure. So we could just say that
we will treat VM_BUG_ON() as a WARN_ON_ONCE(), and just not kill the
machine.
Because I could easily imagine that somebody *does* treat BUG_ON()
that way, thinking "well, if that BUG_ON() triggers at least it won't
then go off the rails later".
In fact, right now we mark BUG() in such a way that gcc can even take
advantage of the "crash the machine" semantics, because we explicitly
mark the BUG() with "unreachable()".
So what I think we should think about is:
- extending the checkpatch warning to VM_BUG_ON too, to discourage new users.
- look at making BUG_ON() simply be less lethal. Remove the
unrechable(), reorganize how the string is stored, and make it act
more like WARN_ON_ONCE() instead (it's the "rewind_stack_do_exit()"
that ends up causing us to try to kill things, we *could* just try to
stop doing that).
- Instead of adding a BUG_ON_AND_HALT(), we could perhaps add a new
FATAL_ERROR() thing that acts like the current BUG_ON, and *not* call
it something similar (we don't want people doing mindless
conversions!). And that's the one that would do the whole
rewind_stack_do_exit() to kill the process.
But apart from the checkpatch thing, it's actually a pretty big change.
Linus
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BUG_ON() in workingset_node_shadows_dec() triggers Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-04 06:10 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Greg KH <greg@kroah.com> - 2016-10-04 10:20 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Johannes Weiner <hannes@cmpxchg.org> - 2016-10-04 11:40 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-05 03:30 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Johannes Weiner <hannes@cmpxchg.org> - 2016-10-05 11:30 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Johannes Weiner <hannes@cmpxchg.org> - 2016-10-05 11:40 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Jan Kara <jack@suse.cz> - 2016-10-05 12:50 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-05 18:20 +0200
Re: [PATCH] checkpatch: extend BUG warning Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-05 19:10 +0200
[PATCH] checkpatch: extend BUG warning Joe Perches <joe@perches.com> - 2016-10-05 19:10 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Paul Gortmaker <paul.gortmaker@windriver.com> - 2016-10-05 04:50 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-05 05:30 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Willy Tarreau <w@1wt.eu> - 2016-10-05 07:50 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-05 18:00 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Willy Tarreau <w@1wt.eu> - 2016-10-05 21:10 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-05 21:20 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Willy Tarreau <w@1wt.eu> - 2016-10-05 23:20 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Kees Cook <keescook@chromium.org> - 2016-10-05 23:20 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-05 23:50 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Kees Cook <keescook@chromium.org> - 2016-10-06 00:20 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-06 00:40 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Kees Cook <keescook@chromium.org> - 2016-10-07 00:10 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-07 00:30 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Kees Cook <keescook@chromium.org> - 2016-10-07 01:10 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-07 02:00 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Willy Tarreau <w@1wt.eu> - 2016-10-07 08:00 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Kees Cook <keescook@chromium.org> - 2016-10-07 19:20 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-07 19:30 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Kees Cook <keescook@chromium.org> - 2016-10-07 19:40 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Willy Tarreau <w@1wt.eu> - 2016-10-07 20:30 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Dave Chinner <david@fromorbit.com> - 2016-10-06 04:10 +0200
Re: BUG_ON() in workingset_node_shadows_dec() triggers Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-06 04:20 +0200
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