| Message ID | 20201028113533.26160-1-lukas.bulwahn@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | net: cls_api: remove unneeded local variable in tc_dump_chain() | expand |
On 10/28/20 4:35 AM, Lukas Bulwahn wrote: > make clang-analyzer on x86_64 defconfig caught my attention with: > > net/sched/cls_api.c:2964:3: warning: Value stored to 'parent' is never read > [clang-analyzer-deadcode.DeadStores] > parent = 0; > ^ > > net/sched/cls_api.c:2977:4: warning: Value stored to 'parent' is never read > [clang-analyzer-deadcode.DeadStores] > parent = q->handle; > ^ > > Commit 32a4f5ecd738 ("net: sched: introduce chain object to uapi") > introduced tc_dump_chain() and this initial implementation already > contained these unneeded dead stores. > > Simplify the code to make clang-analyzer happy. > > As compilers will detect these unneeded assignments and optimize this > anyway, the resulting binary is identical before and after this change. > > No functional change. No change in object code. > > Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com> > --- > applies cleanly on current master and next-20201028 > > Jamal, Cong, Jiri, please ack. > David, Jakub, please pick this minor non-urgent clean-up patch. > > net/sched/cls_api.c | 16 +++------------- > 1 file changed, 3 insertions(+), 13 deletions(-) > > diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c > index faeabff283a2..8ce830ca5f92 100644 > --- a/net/sched/cls_api.c > +++ b/net/sched/cls_api.c > @@ -2940,7 +2940,6 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb) > struct tcf_chain *chain; > long index_start; > long index; > - u32 parent; > int err; > > if (nlmsg_len(cb->nlh) < sizeof(*tcm)) > @@ -2955,13 +2954,6 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb) > block = tcf_block_refcnt_get(net, tcm->tcm_block_index); > if (!block) > goto out; > - /* If we work with block index, q is NULL and parent value > - * will never be used in the following code. The check > - * in tcf_fill_node prevents it. However, compiler does not > - * see that far, so set parent to zero to silence the warning > - * about parent being uninitialized. > - */ > - parent = 0; > } else { > const struct Qdisc_class_ops *cops; > struct net_device *dev; > @@ -2971,13 +2963,11 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb) > if (!dev) > return skb->len; > > - parent = tcm->tcm_parent; > - if (!parent) { > + if (!tcm->tcm_parent) > q = dev->qdisc; > - parent = q->handle; This looks like a an unused error handler. and the later call to if (TC_H_MIN(tcm->tcm_parent) maybe should be if (TC_H_MIN(parent)) so I am skeptical that this change is ok because the code around it looks buggy. Tom > - } else { > + else > q = qdisc_lookup(dev, TC_H_MAJ(tcm->tcm_parent)); > - } > + > if (!q) > goto out; > cops = q->ops->cl_ops; -=-=-=-=-=-=-=-=-=-=-=- Links: You receive all messages sent to this group. View/Reply Online (#131): https://lists.elisa.tech/g/linux-safety/message/131 Mute This Topic: https://lists.elisa.tech/mt/77860764/4688437 Group Owner: linux-safety+owner@lists.elisa.tech Unsubscribe: https://lists.elisa.tech/g/linux-safety/unsub [patchwork-linux-safety@patchwork.kernel.org] -=-=-=-=-=-=-=-=-=-=-=-
On Wed, 28 Oct 2020, Tom Rix wrote: > > On 10/28/20 4:35 AM, Lukas Bulwahn wrote: > > make clang-analyzer on x86_64 defconfig caught my attention with: > > > > net/sched/cls_api.c:2964:3: warning: Value stored to 'parent' is never read > > [clang-analyzer-deadcode.DeadStores] > > parent = 0; > > ^ > > > > net/sched/cls_api.c:2977:4: warning: Value stored to 'parent' is never read > > [clang-analyzer-deadcode.DeadStores] > > parent = q->handle; > > ^ > > > > Commit 32a4f5ecd738 ("net: sched: introduce chain object to uapi") > > introduced tc_dump_chain() and this initial implementation already > > contained these unneeded dead stores. > > > > Simplify the code to make clang-analyzer happy. > > > > As compilers will detect these unneeded assignments and optimize this > > anyway, the resulting binary is identical before and after this change. > > > > No functional change. No change in object code. > > > > Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com> > > --- > > applies cleanly on current master and next-20201028 > > > > Jamal, Cong, Jiri, please ack. > > David, Jakub, please pick this minor non-urgent clean-up patch. > > > > net/sched/cls_api.c | 16 +++------------- > > 1 file changed, 3 insertions(+), 13 deletions(-) > > > > diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c > > index faeabff283a2..8ce830ca5f92 100644 > > --- a/net/sched/cls_api.c > > +++ b/net/sched/cls_api.c > > @@ -2940,7 +2940,6 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb) > > struct tcf_chain *chain; > > long index_start; > > long index; > > - u32 parent; > > int err; > > > > if (nlmsg_len(cb->nlh) < sizeof(*tcm)) > > @@ -2955,13 +2954,6 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb) > > block = tcf_block_refcnt_get(net, tcm->tcm_block_index); > > if (!block) > > goto out; > > - /* If we work with block index, q is NULL and parent value > > - * will never be used in the following code. The check > > - * in tcf_fill_node prevents it. However, compiler does not > > - * see that far, so set parent to zero to silence the warning > > - * about parent being uninitialized. > > - */ > > - parent = 0; > > } else { > > const struct Qdisc_class_ops *cops; > > struct net_device *dev; > > @@ -2971,13 +2963,11 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb) > > if (!dev) > > return skb->len; > > > > - parent = tcm->tcm_parent; > > - if (!parent) { > > + if (!tcm->tcm_parent) > > q = dev->qdisc; > > - parent = q->handle; > > This looks like a an unused error handler. > > and the later call to > > if (TC_H_MIN(tcm->tcm_parent) > > maybe should be > > if (TC_H_MIN(parent)) > > so I am skeptical that this change is ok because the code around it looks buggy. > Maybe that is the case. Certainly the comment above about being uninitialized is outdated as parent is not used in tc_chain_fill_node(). I had another look and I noticed a copy of this same pattern (with the same comment) in tc_dump_tfilter(), but it seems that the two copies have somehow diverged over time. Certainly, something is fishy here. I guess it needs some more digging in the code... Lukas > Tom > > > - } else { > > + else > > q = qdisc_lookup(dev, TC_H_MAJ(tcm->tcm_parent)); > > - } > > + > > if (!q) > > goto out; > > cops = q->ops->cl_ops; > > -=-=-=-=-=-=-=-=-=-=-=- Links: You receive all messages sent to this group. View/Reply Online (#133): https://lists.elisa.tech/g/linux-safety/message/133 Mute This Topic: https://lists.elisa.tech/mt/77860764/4688437 Group Owner: linux-safety+owner@lists.elisa.tech Unsubscribe: https://lists.elisa.tech/g/linux-safety/unsub [patchwork-linux-safety@patchwork.kernel.org] -=-=-=-=-=-=-=-=-=-=-=-
On Wed, Oct 28, 2020 at 6:59 AM Tom Rix <trix@redhat.com> wrote: > > > On 10/28/20 4:35 AM, Lukas Bulwahn wrote: > > @@ -2971,13 +2963,11 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb) > > if (!dev) > > return skb->len; > > > > - parent = tcm->tcm_parent; > > - if (!parent) { > > + if (!tcm->tcm_parent) > > q = dev->qdisc; > > - parent = q->handle; > > This looks like a an unused error handler. > > and the later call to > > if (TC_H_MIN(tcm->tcm_parent) > > maybe should be > > if (TC_H_MIN(parent)) When tcm->tcm_parent is 0, TC_H_MIN(tcm->tcm_parent) is also 0, so we will not hit that if branch. So, I think Lukas' patch is correct. Thanks. -=-=-=-=-=-=-=-=-=-=-=- Links: You receive all messages sent to this group. View/Reply Online (#134): https://lists.elisa.tech/g/linux-safety/message/134 Mute This Topic: https://lists.elisa.tech/mt/77860764/4688437 Group Owner: linux-safety+owner@lists.elisa.tech Unsubscribe: https://lists.elisa.tech/g/linux-safety/unsub [patchwork-linux-safety@patchwork.kernel.org] -=-=-=-=-=-=-=-=-=-=-=-
On Wed, 28 Oct 2020 12:35:33 +0100 Lukas Bulwahn wrote: > make clang-analyzer on x86_64 defconfig caught my attention with: > > net/sched/cls_api.c:2964:3: warning: Value stored to 'parent' is never read > [clang-analyzer-deadcode.DeadStores] > parent = 0; > ^ > > net/sched/cls_api.c:2977:4: warning: Value stored to 'parent' is never read > [clang-analyzer-deadcode.DeadStores] > parent = q->handle; > ^ > > Commit 32a4f5ecd738 ("net: sched: introduce chain object to uapi") > introduced tc_dump_chain() and this initial implementation already > contained these unneeded dead stores. > > Simplify the code to make clang-analyzer happy. > > As compilers will detect these unneeded assignments and optimize this > anyway, the resulting binary is identical before and after this change. > > No functional change. No change in object code. > > Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com> > --- > applies cleanly on current master and next-20201028 > > Jamal, Cong, Jiri, please ack. > David, Jakub, please pick this minor non-urgent clean-up patch. Applied, thanks! -=-=-=-=-=-=-=-=-=-=-=- Links: You receive all messages sent to this group. View/Reply Online (#140): https://lists.elisa.tech/g/linux-safety/message/140 Mute This Topic: https://lists.elisa.tech/mt/77860764/4688437 Group Owner: linux-safety+owner@lists.elisa.tech Unsubscribe: https://lists.elisa.tech/g/linux-safety/unsub [patchwork-linux-safety@patchwork.kernel.org] -=-=-=-=-=-=-=-=-=-=-=-
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c index faeabff283a2..8ce830ca5f92 100644 --- a/net/sched/cls_api.c +++ b/net/sched/cls_api.c @@ -2940,7 +2940,6 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb) struct tcf_chain *chain; long index_start; long index; - u32 parent; int err; if (nlmsg_len(cb->nlh) < sizeof(*tcm)) @@ -2955,13 +2954,6 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb) block = tcf_block_refcnt_get(net, tcm->tcm_block_index); if (!block) goto out; - /* If we work with block index, q is NULL and parent value - * will never be used in the following code. The check - * in tcf_fill_node prevents it. However, compiler does not - * see that far, so set parent to zero to silence the warning - * about parent being uninitialized. - */ - parent = 0; } else { const struct Qdisc_class_ops *cops; struct net_device *dev; @@ -2971,13 +2963,11 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb) if (!dev) return skb->len; - parent = tcm->tcm_parent; - if (!parent) { + if (!tcm->tcm_parent) q = dev->qdisc; - parent = q->handle; - } else { + else q = qdisc_lookup(dev, TC_H_MAJ(tcm->tcm_parent)); - } + if (!q) goto out; cops = q->ops->cl_ops;
make clang-analyzer on x86_64 defconfig caught my attention with: net/sched/cls_api.c:2964:3: warning: Value stored to 'parent' is never read [clang-analyzer-deadcode.DeadStores] parent = 0; ^ net/sched/cls_api.c:2977:4: warning: Value stored to 'parent' is never read [clang-analyzer-deadcode.DeadStores] parent = q->handle; ^ Commit 32a4f5ecd738 ("net: sched: introduce chain object to uapi") introduced tc_dump_chain() and this initial implementation already contained these unneeded dead stores. Simplify the code to make clang-analyzer happy. As compilers will detect these unneeded assignments and optimize this anyway, the resulting binary is identical before and after this change. No functional change. No change in object code. Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com> --- applies cleanly on current master and next-20201028 Jamal, Cong, Jiri, please ack. David, Jakub, please pick this minor non-urgent clean-up patch. net/sched/cls_api.c | 16 +++------------- 1 file changed, 3 insertions(+), 13 deletions(-)