On 25.08.22 13:43, Jani Nikula wrote:

On Thu, 25 Aug 2022, David Hildenbrand [off-list ref] wrote:

quoted

On 24.08.22 18:52, Joe Perches wrote:

quoted

On Wed, 2022-08-24 at 18:31 +0200, David Hildenbrand wrote:

quoted

checkpatch does not point out that VM_BUG_ON() and friends should be
avoided, however, Linus notes:

    VM_BUG_ON() has the exact same semantics as BUG_ON. It is literally
    no different, the only difference is "we can make the code smaller
    because these are less important". [1]

So let's warn on VM_BUG_ON() and friends as well. While at it, make it
clearer that the kernel really shouldn't be crashed.

Note that there are some other *_BUG_ON flavors, but they are not all
bad: for example, KVM_BUG_ON() only triggers a WARN_ON_ONCE and then
flags KVM as being buggy, so we'll not care about them for now here.

[]

quoted

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl

[]

quoted

@@ -4695,12 +4695,12 @@ sub process {
 			}
 		}
 
-# avoid BUG() or BUG_ON()
-		if ($line =~ /\b(?:BUG|BUG_ON)\b/) {
+# do not use BUG(), BUG_ON(), VM_BUG_ON() and friends.
+		if ($line =~ /\b(?:BUG|BUG_ON|VM_BUG_ON|VM_BUG_ON_[A-Z]+)\b/) {

Perhaps better as something like the below to pick up more variants

Trying to find more possible variants and exceptions

quoted

CI_BUG_ON(
-> Bad with CONFIG_DRM_I915_DEBUG
GEM_BUG_ON(
-> Bad with CONFIG_DRM_I915_DEBUG_GEM_ONCE

These are hidden behind debug knobs that we use in our CI to
specifically catch "should not happen" cases fast and loud. Should not
be a problem for regular users.

I tend to agree but I don't think this is worth an exception.
VM_BUG_ON also requires CONFIG_DEBUG_VM and absolutely shouldn't
be used as I learned.

Quoting Linus:

   Really. BUG_ON() IS NOT FOR DEBUGGING. [1]

   This kind of "I don't think this can happen" is _never_ an excuse for it. [2]


For CI work, it might be sufficient to use WARN_ON_ONCE() combined with panic_on_warn.

[1] https://lore.kernel.org/all/CAHk-=wiEAH+ojSpAgx_Ep=NKPWHU8AdO3V56BXcCsU97oYJ1EA@mail.gmail.com/ (local)
[2] https://lore.kernel.org/all/CAHk-=wg40EAZofO16Eviaj7mfqDhZ2gVEbvfsMf6gYzspRjYvw@mail.gmail.com/ (local) 

-- 
Thanks,

David / dhildenb