On Wed, 06 May 2015 11:29:57 +0000 (GMT) Maninder Singh
<maninder...@samsung.com> wrote:
> EP-F6AA0618C49C4AEDA73BFF1B39950BAB
>
> Hi ,
>
> Recently shared a patch for using freezable_schedule instead of schedule in
> msgrcv,
> and after analysing message queuie implemntation we have realized even msgsnd
> can also block, if queue is full,
> So in this scenerio msgsnd sets task state as TASK_INTERRUPTIBLE and can
> schedule function, similar behaviour as msgrcv.
> This change is applicable for msgsnd as well.
>
> we have created patch for remotes/linux-next/akpm, because msgrcv patch is
> already applied at this branch.
> so we didnt include <linux/freezer.h>
>
This changelog is quite poor. It doesn't explain why the change is
being made, it doesn't explain the user-visible effects which are being
fixed, etc.
So I threw it away and copied text from "ipc/msg.c: use freezable
blocking call":
One thing which isn't clear to me: *why* do we want to "Avoid waking up
every thread sleeping in XXX during suspend and resume"? Suspend and
resume are rare operations. Why do we care if a few threads wake up
then go to sleep again?
From: Maninder Singh <maninder...@samsung.com>
Subject: ipc/msg.c: msgsnd: use freezable blocking call
Avoid waking up every thread sleeping in a msgsnd call during suspend and
resume by calling a freezable blocking call. Previous patches modified
the freezer to avoid sending wakeups to threads that are blocked in
freezable blocking calls.
This call was selected to be converted to a freezable call because it
doesn't hold any locks or release any resources when interrupted that
might be needed by another freezing task or a kernel driver during
suspend, and is a common site where idle userspace tasks are blocked.
Signed-off-by: Vaneet narang <v.nar...@samsung.com>
Signed-off-by: Maninder Singh <maninder...@samsung.com>
Cc: Yogesh Gaur <yn.g...@samsung.com>
Cc: Manjeet Pawar <manjee...@samsung.com>
Cc: Ajeet Yadav <ajee...@samsung.com>
Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
Cc: Tejun Heo <t...@kernel.org>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
---
ipc/msg.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN ipc/msg.c~ipc-msgc-msgsnd-use-freezable-blocking-call ipc/msg.c
--- a/ipc/msg.c~ipc-msgc-msgsnd-use-freezable-blocking-call
+++ a/ipc/msg.c
@@ -673,7 +673,7 @@ long do_msgsnd(int msqid, long mtype, vo
ipc_unlock_object(&msq->q_perm);
rcu_read_unlock();
- schedule();
+ freezable_schedule();
rcu_read_lock();
ipc_lock_object(&msq->q_perm);
_
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