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Date: Tue, 09 Apr 2013 11:39:07 +0200
From: Nikola Pajkovsky <npajkovs@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Stanislav Kinsbursky <skinsbursky@...allels.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Peter Hurley <peter@...leysoftware.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipc: use list_for_each_entry for list traversing
Andrew Morton <akpm@...ux-foundation.org> writes:
> On Fri, 5 Apr 2013 15:42:11 +0200 Nikola Pajkovsky <npajkovs@...hat.com> wrote:
>
>> the ipc/msg.c code does all list operations by hand and it open-codes
>> the accesses, instead of using for_each_entry.
>>
>> ...
>>
>> --- a/ipc/msg.c
>> +++ b/ipc/msg.c
>> @@ -237,14 +237,9 @@ static inline void ss_del(struct msg_sender *mss)
>>
>> static void ss_wakeup(struct list_head *h, int kill)
>> {
>> - struct list_head *tmp;
>> + struct msg_sender *mss, *t;
>>
>> - tmp = h->next;
>> - while (tmp != h) {
>> - struct msg_sender *mss;
>> -
>> - mss = list_entry(tmp, struct msg_sender, list);
>> - tmp = tmp->next;
>> + list_for_each_entry_safe(mss, t, h, list) {
>> if (kill)
>> mss->list.next = NULL;
>> wake_up_process(mss->tsk);
>
> urgh, that code is sick. What's it doing poking around in the
> list_head internals?
No idea, it there from beginning of first kernel importation into
git. Where is history before git?
>> @@ -253,14 +248,9 @@ static void ss_wakeup(struct list_head *h, int kill)
>>
>> static void expunge_all(struct msg_queue *msq, int res)
>> {
>> - struct list_head *tmp;
>> -
>> - tmp = msq->q_receivers.next;
>> - while (tmp != &msq->q_receivers) {
>> - struct msg_receiver *msr;
>> + struct msg_receiver *msr, *t;
>>
>> - msr = list_entry(tmp, struct msg_receiver, r_list);
>> - tmp = tmp->next;
>> + list_for_each_entry_safe(msr, t, &msq->q_receivers, r_list) {
>> msr->r_msg = NULL;
>> wake_up_process(msr->r_tsk);
>> smp_mb();
>
> I think list_for_each_entry() would suffice here.
I don't know, I found wake_up_sem_queue_do in sem.c and it looks almost same
except preempt stuff. I'll be dancing around ipc/
>> @@ -278,7 +268,7 @@ static void expunge_all(struct msg_queue *msq, int res)
>> */
>> static void freeque(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
>> {
>> - struct list_head *tmp;
>> + struct msg_msg *msg;
>> struct msg_queue *msq = container_of(ipcp, struct msg_queue, q_perm);
>>
>> expunge_all(msq, -EIDRM);
>> @@ -286,11 +276,7 @@ static void freeque(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
>> msg_rmid(ns, msq);
>> msg_unlock(msq);
>>
>> - tmp = msq->q_messages.next;
>> - while (tmp != &msq->q_messages) {
>> - struct msg_msg *msg = list_entry(tmp, struct msg_msg, m_list);
>> -
>> - tmp = tmp->next;
>> + list_for_each_entry(msg, &msq->q_messages, m_list) {
>> atomic_dec(&ns->msg_hdrs);
>> free_msg(msg);
>> }
>
> This is buggy isn't it? list_for_each_entry() will use the
> recently-freed `msg'.
yes, it is.
--8<-----8<-----8<-----8<-----8<-----8<---
From: Nikola Pajkovsky <npajkovs@...hat.com>
Date: Thu, 4 Apr 2013 19:23:55 +0200
Subject: [PATCH v2] ipc: use list_for_each_entry_[safe] for list traversing
the ipc/msg.c code does all list operations by hand and it open-codes
the accesses, instead of using for_each_entry_[safe].
v2: in freeque there has to be used safe version of list_for_each_entry
Signed-off-by: Nikola Pajkovsky <npajkovs@...hat.com>
---
ipc/msg.c | 35 ++++++++---------------------------
1 files changed, 8 insertions(+), 27 deletions(-)
diff --git a/ipc/msg.c b/ipc/msg.c
index fede1d0..f45ef14 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -237,14 +237,9 @@ static inline void ss_del(struct msg_sender *mss)
static void ss_wakeup(struct list_head *h, int kill)
{
- struct list_head *tmp;
+ struct msg_sender *mss, *t;
- tmp = h->next;
- while (tmp != h) {
- struct msg_sender *mss;
-
- mss = list_entry(tmp, struct msg_sender, list);
- tmp = tmp->next;
+ list_for_each_entry_safe(mss, t, h, list) {
if (kill)
mss->list.next = NULL;
wake_up_process(mss->tsk);
@@ -253,14 +248,9 @@ static void ss_wakeup(struct list_head *h, int kill)
static void expunge_all(struct msg_queue *msq, int res)
{
- struct list_head *tmp;
-
- tmp = msq->q_receivers.next;
- while (tmp != &msq->q_receivers) {
- struct msg_receiver *msr;
+ struct msg_receiver *msr, *t;
- msr = list_entry(tmp, struct msg_receiver, r_list);
- tmp = tmp->next;
+ list_for_each_entry_safe(msr, t, &msq->q_receivers, r_list) {
msr->r_msg = NULL;
wake_up_process(msr->r_tsk);
smp_mb();
@@ -278,7 +268,7 @@ static void expunge_all(struct msg_queue *msq, int res)
*/
static void freeque(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
{
- struct list_head *tmp;
+ struct msg_msg *msg, *t;
struct msg_queue *msq = container_of(ipcp, struct msg_queue, q_perm);
expunge_all(msq, -EIDRM);
@@ -286,11 +276,7 @@ static void freeque(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
msg_rmid(ns, msq);
msg_unlock(msq);
- tmp = msq->q_messages.next;
- while (tmp != &msq->q_messages) {
- struct msg_msg *msg = list_entry(tmp, struct msg_msg, m_list);
-
- tmp = tmp->next;
+ list_for_each_entry_safe(msg, t, &msq->q_messages, m_list) {
atomic_dec(&ns->msg_hdrs);
free_msg(msg);
}
@@ -602,14 +588,9 @@ static int testmsg(struct msg_msg *msg, long type, int mode)
static inline int pipelined_send(struct msg_queue *msq, struct msg_msg *msg)
{
- struct list_head *tmp;
-
- tmp = msq->q_receivers.next;
- while (tmp != &msq->q_receivers) {
- struct msg_receiver *msr;
+ struct msg_receiver *msr, *t;
- msr = list_entry(tmp, struct msg_receiver, r_list);
- tmp = tmp->next;
+ list_for_each_entry_safe(msr, t, &msq->q_receivers, r_list) {
if (testmsg(msg, msr->r_msgtype, msr->r_mode) &&
!security_msg_queue_msgrcv(msq, msg, msr->r_tsk,
msr->r_msgtype, msr->r_mode)) {
--
1.7.1
--
Nikola
--
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