Messages in this thread | | | Date | Thu, 1 Nov 2018 18:17:19 -0400 (EDT) | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH for 4.21 03/16] mm: Replace BUG_ON() by WARN_ON() in vm_unmap_ram() |
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----- On Nov 1, 2018, at 11:00 PM, Linus Torvalds torvalds@linux-foundation.org wrote:
> On Thu, Nov 1, 2018 at 12:57 PM Mathieu Desnoyers > <mathieu.desnoyers@efficios.com> wrote: >> >> > I think the graceful recovery is to simply return: >> > >> > if (WARN_ON(cond)) >> > return; >> > >> > is better than just >> > >> > BUG_ON(cond); >> > >> > As that's what Linus made pretty clear at the Maintainer's Summit. >> >> That's it. For an unmap function, this basically boils down to >> print a warning and leak the memory on internal unmap error. >> >> I will update the commit message describing this behavior. > > It might be even better to use WARN_ON_ONCE(). > > If it's a "this shouldn't happen" situation, the advantage of > WARN_ON_ONCE() is that it will still show the backtrace of the "how > the heck did it happen after all" situation, but if it turns ouit to > be user-triggerable (or simply triggerable by some odd hw situation), > it won't spam your logs forever. > > Obviously, things like rate limiting etc can also be good ideas, but > that's just overkill for "this really should never happen" cases. > > (Side note: WARN_ON_ONCE() will _warn_ just once, but will always > return the condition that it warns for, so the return value is _not_ > "I have warned", but "I have seen the condition that I should warn > about". Just in case people are worried about it).
Allright, I'll update this patch (and the following one implementing vm_{map,unmap}_user_ram) to use WARN_ON_ONCE().
Thanks!
Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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