From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3F9AE208971 for ; Fri, 18 Oct 2024 18:22:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729275737; cv=none; b=GRYB6CBf4A+CNk1yfK65a+lY1lHyE1/D26sXksX3XFgw4s0C6vBc+vJdhX73Mq3nG+PiIU8Du3hzAe9jF5zVymLwwlSlNxt4PD6IpSqrDBe6IZ75aLWBujVdt+ZklqtYrNryoYaL+gl8wQWM4UBMJOFm35LkYyHX/fS/XodCbPY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729275737; c=relaxed/simple; bh=fsaUa9G1opCeUihrjrdTRgCV45Ou5JI4JRd24hmNsBg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=A6damkJtowbVLreTyE627M+Y7Blq/KXcWEg9vaA5ICc8dWSeMl5MNw2jsJApKwutvdfIjVuuCcBPLYmyGWuvhSXz6JDxnAg3GYmbYF+EFCp+ZF/C1E5FVo5LUexxGckFhiKBxTlza9ngnfytEFN+SgZS9FgNNOl9uk1vzByOj6o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=ISWYdl7x; arc=none smtp.client-ip=91.218.175.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="ISWYdl7x" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1729275733; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=aX3NnUn3UeH6nxlGLDibU44GfunoKuAgfBARM5Nx6YQ=; b=ISWYdl7xe2RCvWWdBZlzAuQHys34NaB91RlKHoJSftbAhIcBUgKd3W1Au95yy4fSCqFl56 K51phyfbeZytnF7akWTGEJj2x2Nap8e4ON+XOBd1ZPhR+9Jgtj+RkSC4ZcRnI+vedNFPgD HT+31mMysD4cFpNox6amsUooFVTqBKI= Date: Fri, 18 Oct 2024 11:22:00 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next 1/2] bpf: Add open coded version of kmem_cache iterator To: Namhyung Kim 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 References: <20241017080604.541872-1-namhyung@kernel.org> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau Content-Language: en-US In-Reply-To: <20241017080604.541872-1-namhyung@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT 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? > + 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) > {