| Message ID | 20181104125028.3572-1-tiny.windzz@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm, slab: remove unnecessary unlikely() | expand |
+CC Dmitry On 11/4/18 1:50 PM, Yangtao Li wrote: > WARN_ON() already contains an unlikely(), so it's not necessary to use > unlikely. > > Signed-off-by: Yangtao Li <tiny.windzz@gmail.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Maybe also change it back to WARN_ON_ONCE? I already considered it while reviewing Dmitry's patch and wasn't sure. Now I think that what can happen is that either a kernel bug is introduced that _ONCE is enough to catch (two separate bugs introduced to both hit this would be rare, and in that case the second one will be reported after the first one is fixed), or this gets called with a user-supplied value, and then we want to avoid spamming dmesg with multiple warnings that the user could trigger at will. > --- > mm/slab_common.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 7eb8dc136c1c..4f54684f5435 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -1029,10 +1029,8 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags) > > index = size_index[size_index_elem(size)]; > } else { > - if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) { > - WARN_ON(1); > + if (WARN_ON(size > KMALLOC_MAX_CACHE_SIZE)) > return NULL; > - } > index = fls(size - 1); > } > >
On Mon, Nov 5, 2018 at 11:18 AM, Vlastimil Babka <vbabka@suse.cz> wrote: > +CC Dmitry > > On 11/4/18 1:50 PM, Yangtao Li wrote: >> WARN_ON() already contains an unlikely(), so it's not necessary to use >> unlikely. >> >> Signed-off-by: Yangtao Li <tiny.windzz@gmail.com> > > Acked-by: Vlastimil Babka <vbabka@suse.cz> > > Maybe also change it back to WARN_ON_ONCE? I already considered it while > reviewing Dmitry's patch and wasn't sure. Now I think that what can > happen is that either a kernel bug is introduced that _ONCE is enough to > catch (two separate bugs introduced to both hit this would be rare, and > in that case the second one will be reported after the first one is > fixed), or this gets called with a user-supplied value, and then we want > to avoid spamming dmesg with multiple warnings that the user could > trigger at will. If you asking me, I am fine both changes. I was mainly interested in removing the bogus warnings that actually fire. >> --- >> mm/slab_common.c | 4 +--- >> 1 file changed, 1 insertion(+), 3 deletions(-) >> >> diff --git a/mm/slab_common.c b/mm/slab_common.c >> index 7eb8dc136c1c..4f54684f5435 100644 >> --- a/mm/slab_common.c >> +++ b/mm/slab_common.c >> @@ -1029,10 +1029,8 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags) >> >> index = size_index[size_index_elem(size)]; >> } else { >> - if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) { >> - WARN_ON(1); >> + if (WARN_ON(size > KMALLOC_MAX_CACHE_SIZE)) >> return NULL; >> - } >> index = fls(size - 1); >> } >> >> >
On 11/6/18 6:38 AM, Dmitry Vyukov wrote: > On Mon, Nov 5, 2018 at 11:18 AM, Vlastimil Babka <vbabka@suse.cz> wrote: >> +CC Dmitry >> >> On 11/4/18 1:50 PM, Yangtao Li wrote: >>> WARN_ON() already contains an unlikely(), so it's not necessary to use >>> unlikely. >>> >>> Signed-off-by: Yangtao Li <tiny.windzz@gmail.com> >> >> Acked-by: Vlastimil Babka <vbabka@suse.cz> >> >> Maybe also change it back to WARN_ON_ONCE? I already considered it while >> reviewing Dmitry's patch and wasn't sure. Now I think that what can >> happen is that either a kernel bug is introduced that _ONCE is enough to >> catch (two separate bugs introduced to both hit this would be rare, and >> in that case the second one will be reported after the first one is >> fixed), or this gets called with a user-supplied value, and then we want >> to avoid spamming dmesg with multiple warnings that the user could >> trigger at will. > > > If you asking me, I am fine both changes. > I was mainly interested in removing the bogus warnings that actually fire. OK thanks. Andrew can you update the patch to WARN_ON_ONCE? Changelog addition: Also change WARN_ON() back to WARN_ON_ONCE() to avoid potentially spamming dmesg with user-triggerable large allocations. > >>> --- >>> mm/slab_common.c | 4 +--- >>> 1 file changed, 1 insertion(+), 3 deletions(-) >>> >>> diff --git a/mm/slab_common.c b/mm/slab_common.c >>> index 7eb8dc136c1c..4f54684f5435 100644 >>> --- a/mm/slab_common.c >>> +++ b/mm/slab_common.c >>> @@ -1029,10 +1029,8 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags) >>> >>> index = size_index[size_index_elem(size)]; >>> } else { >>> - if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) { >>> - WARN_ON(1); >>> + if (WARN_ON(size > KMALLOC_MAX_CACHE_SIZE)) >>> return NULL; >>> - } >>> index = fls(size - 1); >>> } >>> >>> >>
On Sun, 4 Nov 2018, Yangtao Li wrote: > WARN_ON() already contains an unlikely(), so it's not necessary to use > unlikely. > > Signed-off-by: Yangtao Li <tiny.windzz@gmail.com> Acked-by: David Rientjes <rientjes@google.com>
diff --git a/mm/slab_common.c b/mm/slab_common.c index 7eb8dc136c1c..4f54684f5435 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -1029,10 +1029,8 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags) index = size_index[size_index_elem(size)]; } else { - if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) { - WARN_ON(1); + if (WARN_ON(size > KMALLOC_MAX_CACHE_SIZE)) return NULL; - } index = fls(size - 1); }
WARN_ON() already contains an unlikely(), so it's not necessary to use unlikely. Signed-off-by: Yangtao Li <tiny.windzz@gmail.com> --- mm/slab_common.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)