linux-kernel - Re: [PATCH] lib/dynamic_queue_limits.c: relax BUG_ON to WARN_ON in dql

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Message-ID: <1508352351.31614.127.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Wed, 18 Oct 2017 11:45:51 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] lib/dynamic_queue_limits.c: relax BUG_ON to WARN_ON in
 dql_complete()

On Wed, 2017-10-18 at 18:57 +0100, Ard Biesheuvel wrote:
> On 18 October 2017 at 17:29, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > On Wed, 2017-10-18 at 16:45 +0100, Ard Biesheuvel wrote:
> >> Even though calling dql_completed() with a count that exceeds the
> >> queued count is a serious error, it still does not justify bringing
> >> down the entire kernel with a BUG_ON(). So relax it to a WARN_ON()
> >> instead.
> >>
> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> >> ---
> >>  lib/dynamic_queue_limits.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/lib/dynamic_queue_limits.c b/lib/dynamic_queue_limits.c
> >> index f346715e2255..24ce495d78f3 100644
> >> --- a/lib/dynamic_queue_limits.c
> >> +++ b/lib/dynamic_queue_limits.c
> >> @@ -23,7 +23,7 @@ void dql_completed(struct dql *dql, unsigned int count)
> >>       num_queued = ACCESS_ONCE(dql->num_queued);
> >>
> >>       /* Can't complete more than what's in queue */
> >> -     BUG_ON(count > num_queued - dql->num_completed);
> >> +     WARN_ON(count > num_queued - dql->num_completed);
> >>
> >>       completed = dql->num_completed + count;
> >>       limit = dql->limit;
> >
> > So instead fixing the faulty driver, you'll have strange lockups, and
> > force your users to reboot anyway, after annoying periods where
> > "Internet does not work"
> >
> > These kinds of errors should be found when testing a new device driver
> > or new kernel.
> >
> > Have you found the root cause ?
> >
> 
> Not yet, and I don't intend to send out any patches for this
> particular hardware until this is fixed.
> 
> But that still doesn't mean you should crash hard. As Linus puts it,
> it is better to 'limp on' if you can (unless we're likely to corrupt
> any non-volatile data, e.g., files on disk etc)

How many BUG() do you plan to change to WARN() exactly ?

If you want to comply to Linus wish, just compile your kernel
with appropriate option.

CONFIG_BUG=n