Messages in this thread Patch in this message | | | Date | Wed, 24 Nov 2021 14:45:59 -0800 | Subject | Re: [PATCH] mm: Use BUG_ON instead of if condition followed by BUG | From | John Hubbard <> |
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On 11/24/21 14:27, Andrew Morton wrote: > On Wed, 24 Nov 2021 13:23:42 +0000 Matthew Wilcox <willy@infradead.org> wrote: > >> On Wed, Nov 24, 2021 at 03:08:49AM +0000, cgel.zte@gmail.com wrote: >>> From: chiminghao <chi.minghao@zte.com.cn> >>> >>> Fix the following coccinelle report: >>> ./mm/memory_hotplug.c:2210:2-5: >>> WARNING Use BUG_ON instead of if condition followed by BUG. >> >> What coccinelle script is reporting this? >> >>> - if (try_remove_memory(start, size)) >>> - BUG(); >>> + BUG_ON(try_remove_memory(start, size)); >> >> I really, really, really do not like this. For functions with >> side-effects, this is bad style. If it's a pure predicate, then >> sure, but this is bad. > > I don't like it either. Yes, BUG() is special but it's such dangerous > practice. I'd vote to change coccinelle. >
Definitely! Or at least use a safer pattern/habit, with just a passive variable in the BUG_ON() call, approximately like this:
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 852041f6be41..48bd5ff341e7 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -2201,13 +2201,12 @@ static int __ref try_remove_memory(u64 start, u64 size) */ void __remove_memory(u64 start, u64 size) { - + int ret = try_remove_memory(start, size); /* * trigger BUG() if some memory is not offlined prior to calling this * function */ - if (try_remove_memory(start, size)) - BUG(); + BUG_ON(ret); }
/*
...and by the way, while going to type that, I immediately stumbled upon another pre-existing case of this sort of thing, in try_remove_memory(), which does this:
static int __ref try_remove_memory(u64 start, u64 size) { struct vmem_altmap mhp_altmap = {}; struct vmem_altmap *altmap = NULL; unsigned long nr_vmemmap_pages; int rc = 0, nid = NUMA_NO_NODE;
BUG_ON(check_hotplug_memory_range(start, size));
...
thanks, -- John Hubbard NVIDIA
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