Subject: [merged] ipcmsg-document-barriers.patch removed from -mm tree
To: davidlohr@xxxxxx,aswin@xxxxxx,manfred@xxxxxxxxxxxxxxxx,riel@xxxxxxxxxx,mm-commits@xxxxxxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Tue, 28 Jan 2014 11:09:41 -0800
The patch titled
Subject: ipc,msg: document barriers
has been removed from the -mm tree. Its filename was
ipcmsg-document-barriers.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Davidlohr Bueso <davidlohr@xxxxxx>
Subject: ipc,msg: document barriers
Both expunge_all() and pipeline_send() rely on both a nil msg value and a
full barrier to guarantee the correct ordering when waking up a task.
While its counter part at the receiving end is well documented for the
lockless recv algorithm, we still need to document these specific smp_mb()
calls.
[akpm@xxxxxxxxxxxxxxxxxxxx: fix typo, per Mike]
[akpm@xxxxxxxxxxxxxxxxxxxx: mroe tpyos]
Signed-off-by: Davidlohr Bueso <davidlohr@xxxxxx>
Cc: Aswin Chandramouleeswaran <aswin@xxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/msg.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
diff -puN ipc/msg.c~ipcmsg-document-barriers ipc/msg.c
--- a/ipc/msg.c~ipcmsg-document-barriers
+++ a/ipc/msg.c
@@ -253,8 +253,14 @@ static void expunge_all(struct msg_queue
struct msg_receiver *msr, *t;
list_for_each_entry_safe(msr, t, &msq->q_receivers, r_list) {
- msr->r_msg = NULL;
+ msr->r_msg = NULL; /* initialize expunge ordering */
wake_up_process(msr->r_tsk);
+ /*
+ * Ensure that the wakeup is visible before setting r_msg as
+ * the receiving end depends on it: either spinning on a nil,
+ * or dealing with -EAGAIN cases. See lockless receive part 1
+ * and 2 in do_msgrcv().
+ */
smp_mb();
msr->r_msg = ERR_PTR(res);
}
@@ -638,15 +644,22 @@ static inline int pipelined_send(struct
list_del(&msr->r_list);
if (msr->r_maxsize < msg->m_ts) {
+ /* initialize pipelined send ordering */
msr->r_msg = NULL;
wake_up_process(msr->r_tsk);
- smp_mb();
+ smp_mb(); /* see barrier comment below */
msr->r_msg = ERR_PTR(-E2BIG);
} else {
msr->r_msg = NULL;
msq->q_lrpid = task_pid_vnr(msr->r_tsk);
msq->q_rtime = get_seconds();
wake_up_process(msr->r_tsk);
+ /*
+ * Ensure that the wakeup is visible before
+ * setting r_msg, as the receiving end depends
+ * on it. See lockless receive part 1 and 2 in
+ * do_msgrcv().
+ */
smp_mb();
msr->r_msg = msg;
@@ -654,6 +667,7 @@ static inline int pipelined_send(struct
}
}
}
+
return 0;
}
@@ -716,6 +730,7 @@ long do_msgsnd(int msqid, long mtype, vo
goto out_unlock0;
}
+ /* enqueue the sender and prepare to block */
ss_add(msq, &s);
if (!ipc_rcu_getref(msq)) {
_
Patches currently in -mm which might be from davidlohr@xxxxxx are
origin.patch
linux-next.patch
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