| Message ID | 20211124030849.34998-1-chi.minghao@zte.com.cn (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: Use BUG_ON instead of if condition followed by BUG | expand |
On 24.11.21 04:08, cgel.zte@gmail.com wrote: > From: chiminghao <chi.minghao@zte.com.cn> "mm/memory_hotplug: Use BUG_ON instead of if condition followed by BUG" Would be better > > Fix the following coccinelle report: > ./mm/memory_hotplug.c:2210:2-5: > WARNING Use BUG_ON instead of if condition followed by BUG. > > Reported-by: Zeal Robot <zealci@zte.com.cn> > Signed-off-by: chiminghao <chi.minghao@zte.com.cn> > --- > mm/memory_hotplug.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 3de7933e5302..aecb12bb7513 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -2212,8 +2212,7 @@ void __remove_memory(u64 start, u64 size) > * trigger BUG() if some memory is not offlined prior to calling this > * function > */ > - if (try_remove_memory(start, size)) > - BUG(); > + BUG_ON(try_remove_memory(start, size)); > } > > /* > Acked-by: David Hildenbrand <david@redhat.com>
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.
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.
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,
On Wed, Nov 24, 2021 at 01:23:42PM +0000, Matthew Wilcox 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? Maybe I found it? scripts/coccinelle/misc/bugon.cocci:msg="WARNING: Use BUG_ON instead of if condition followed by BUG.\nPlease make sure the condition has no side effects (see conditional BUG_ON definition in include/asm-generic/bug.h)" Julia, Michal, can we delete this script, please? It's being abused. > > - 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. >
On Wed, Nov 24, 2021 at 02:45:59PM -0800, John Hubbard wrote: > @@ -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); > } I'd rather leave it the way it is. I don't see why the version you propose is better. > ...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)); That needs to be fixed.
On 11/24/21 19:32, Matthew Wilcox wrote: > On Wed, Nov 24, 2021 at 02:45:59PM -0800, John Hubbard wrote: >> @@ -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); >> } > > I'd rather leave it the way it is. I don't see why the version you > propose is better. In isolation, it's *not* better. It's only potentially useful in the context of "code plus tools". That is to say, if the coccinelle change request were rejected, then this provides a way forward that is not worse than the existing code, and also works around the warning. > >> ...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)); > > That needs to be fixed. Yes it does. :) I pointed it out in hopes that Chiminghao might be inspired to go find and fix some of these. thanks,
On Thu, 25 Nov 2021, Matthew Wilcox wrote: > On Wed, Nov 24, 2021 at 01:23:42PM +0000, Matthew Wilcox 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? > > Maybe I found it? > > scripts/coccinelle/misc/bugon.cocci:msg="WARNING: Use BUG_ON instead of if condition followed by BUG.\nPlease make sure the condition has no side effects (see conditional BUG_ON definition in include/asm-generic/bug.h)" > > Julia, Michal, can we delete this script, please? It's being abused. OK julia > > > > - 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. > > >
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 3de7933e5302..aecb12bb7513 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -2212,8 +2212,7 @@ void __remove_memory(u64 start, u64 size) * trigger BUG() if some memory is not offlined prior to calling this * function */ - if (try_remove_memory(start, size)) - BUG(); + BUG_ON(try_remove_memory(start, size)); } /*