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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1729619280; bh=0jeHh94OYCmeLHdHs2fgO2Vhltp9K3H6c/3aZLMOYKQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KolxZ12ktC00Wu2p9wtywMiAAO9nXET8nhdJ/64Cr0GQe3Gwdl8QMQkPC9UKsIRuF 4/y5vLeal4232S2bCaDxcXxPqVCvzfbYWMBg6uMGt1I99r3zoqTkiK+Vdnr5PbpNKJ sb1rV93hMLmad4KXYSOEuUz/gPZ7iL5cxif3eQ01K1DFziDuaGInRfnufVikT8UO13 KwENnZBBKr0je1cvBTcOCg9EkrcsCXlaIy9eRUcgRbvMfLxokjzlIpsTMU/4UEVrLP Q5+E/s7mopkU2KvLhKNjGCovC1hWlEK+IuClOpkwcmg0/VnS8XG4hqlrGQIh/US2HM HDwMiyVFr/obw== Date: Tue, 22 Oct 2024 10:47:57 -0700 From: Namhyung Kim To: Martin KaFai Lau Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , LKML , bpf@vger.kernel.org, Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, Arnaldo Carvalho de Melo , Kees Cook Subject: Re: [PATCH bpf-next 1/2] bpf: Add open coded version of kmem_cache iterator Message-ID: References: <20241017080604.541872-1-namhyung@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 4D5E3A0025 X-Rspamd-Server: rspam01 X-Stat-Signature: nyqpenua8ysnknsdemjnnf53cy3mrscw X-HE-Tag: 1729619270-993506 X-HE-Meta: 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 p0wqx09X UFt8mgi7d3oHp6slDv/5PfB6V4LHUUo5yUj+bpaTvvaf91OYuGYxTJbRW7iMB6GjMt/OzRjhHIJijc/CxVNpyaIf1HOuM6ogleQTAmmZo1uNDMNJBxcJzLBbVS9wM5Gi350ZflWii2wS8z8qkUG4ivr0tNJlv/dGA2RR9ILratnknwlOiWKuXxgq8pBb09ATQv/tGKCPr0gjnatcMUt61gMiDyPBdPWokpwt6ZkkD3jh3W/Z+jLHxLNPdESe1Wm+2c+r27yfe+Ze6+hYQv0dkRAQU+5LC7zJCrwRRdHQFLdOi30PTOkqE4JCxcEPIuErBhEMfUEaKAWxZNfxbPX+CJ0AtulNlBTnwGgymZsi92RZ1WSBPMpCipEg981wUu0yErMg6PfQ8laK2pdM= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello, On Fri, Oct 18, 2024 at 11:22:00AM -0700, Martin KaFai Lau wrote: > On 10/17/24 1:06 AM, Namhyung Kim wrote: > > Add a new open coded iterator for kmem_cache which can be called from a > > BPF program like below. It doesn't take any argument and traverses all > > kmem_cache entries. > > > > struct kmem_cache *pos; > > > > bpf_for_each(kmem_cache, pos) { > > ... > > } > > > > As it needs to grab slab_mutex, it should be called from sleepable BPF > > programs only. > > > > Signed-off-by: Namhyung Kim > > --- > > kernel/bpf/helpers.c | 3 ++ > > kernel/bpf/kmem_cache_iter.c | 87 ++++++++++++++++++++++++++++++++++++ > > 2 files changed, 90 insertions(+) > > > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c > > index 073e6f04f4d765ff..d1dfa4f335577914 100644 > > --- a/kernel/bpf/helpers.c > > +++ b/kernel/bpf/helpers.c > > @@ -3111,6 +3111,9 @@ BTF_ID_FLAGS(func, bpf_iter_bits_next, KF_ITER_NEXT | KF_RET_NULL) > > BTF_ID_FLAGS(func, bpf_iter_bits_destroy, KF_ITER_DESTROY) > > BTF_ID_FLAGS(func, bpf_copy_from_user_str, KF_SLEEPABLE) > > BTF_ID_FLAGS(func, bpf_get_kmem_cache) > > +BTF_ID_FLAGS(func, bpf_iter_kmem_cache_new, KF_ITER_NEW | KF_SLEEPABLE) > > +BTF_ID_FLAGS(func, bpf_iter_kmem_cache_next, KF_ITER_NEXT | KF_RET_NULL | KF_SLEEPABLE) > > +BTF_ID_FLAGS(func, bpf_iter_kmem_cache_destroy, KF_ITER_DESTROY | KF_SLEEPABLE) > > BTF_KFUNCS_END(common_btf_ids) > > static const struct btf_kfunc_id_set common_kfunc_set = { > > diff --git a/kernel/bpf/kmem_cache_iter.c b/kernel/bpf/kmem_cache_iter.c > > index ebc101d7da51b57c..31ddaf452b20a458 100644 > > --- a/kernel/bpf/kmem_cache_iter.c > > +++ b/kernel/bpf/kmem_cache_iter.c > > @@ -145,6 +145,93 @@ static const struct bpf_iter_seq_info kmem_cache_iter_seq_info = { > > .seq_ops = &kmem_cache_iter_seq_ops, > > }; > > +/* open-coded version */ > > +struct bpf_iter_kmem_cache { > > + __u64 __opaque[1]; > > +} __attribute__((aligned(8))); > > + > > +struct bpf_iter_kmem_cache_kern { > > + struct kmem_cache *pos; > > +} __attribute__((aligned(8))); > > + > > +__bpf_kfunc_start_defs(); > > + > > +__bpf_kfunc int bpf_iter_kmem_cache_new(struct bpf_iter_kmem_cache *it) > > +{ > > + struct bpf_iter_kmem_cache_kern *kit = (void *)it; > > + > > + BUILD_BUG_ON(sizeof(*kit) > sizeof(*it)); > > + BUILD_BUG_ON(__alignof__(*kit) != __alignof__(*it)); > > + > > + kit->pos = NULL; > > + return 0; > > +} > > + > > +__bpf_kfunc struct kmem_cache *bpf_iter_kmem_cache_next(struct bpf_iter_kmem_cache *it) > > +{ > > + struct bpf_iter_kmem_cache_kern *kit = (void *)it; > > + struct kmem_cache *prev = kit->pos; > > + struct kmem_cache *next; > > + bool destroy = false; > > + > > + mutex_lock(&slab_mutex); > > I think taking mutex_lock here should be fine since sleepable tracing prog > should be limited to the error injection whitelist. Those functions should > not have held the mutex afaict. > > > + > > + if (list_empty(&slab_caches)) { > > + mutex_unlock(&slab_mutex); > > + return NULL; > > + } > > + > > + if (prev == NULL) > > + next = list_first_entry(&slab_caches, struct kmem_cache, list); > > + else if (list_last_entry(&slab_caches, struct kmem_cache, list) == prev) > > + next = NULL; > > At the last entry, next is NULL. > > > + else > > + next = list_next_entry(prev, list); > > + > > + /* boot_caches have negative refcount, don't touch them */ > > + if (next && next->refcount > 0) > > + next->refcount++; > > + > > + /* Skip kmem_cache_destroy() for active entries */ > > + if (prev && prev->refcount > 1) > > + prev->refcount--; > > + else if (prev && prev->refcount == 1) > > + destroy = true; > > + > > + mutex_unlock(&slab_mutex); > > + > > + if (destroy) > > + kmem_cache_destroy(prev); > > + > > + kit->pos = next; > > so kit->pos will be NULL also. Does it mean the bpf prog will be able to > call bpf_iter_kmem_cache_next() again and re-loop from the beginning of the > slab_caches list? Right, I'll mark the start pos differently to prevent that. Thanks, Namhyung > > > + return next; > > +} > > + > > +__bpf_kfunc void bpf_iter_kmem_cache_destroy(struct bpf_iter_kmem_cache *it) > > +{ > > + struct bpf_iter_kmem_cache_kern *kit = (void *)it; > > + struct kmem_cache *s = kit->pos; > > + bool destroy = false; > > + > > + if (s == NULL) > > + return; > > + > > + mutex_lock(&slab_mutex); > > + > > + /* Skip kmem_cache_destroy() for active entries */ > > + if (s->refcount > 1) > > + s->refcount--; > > + else if (s->refcount == 1) > > + destroy = true; > > + > > + mutex_unlock(&slab_mutex); > > + > > + if (destroy) > > + kmem_cache_destroy(s); > > +} > > + > > +__bpf_kfunc_end_defs(); > > + > > static void bpf_iter_kmem_cache_show_fdinfo(const struct bpf_iter_aux_info *aux, > > struct seq_file *seq) > > { >