Re: [PATCH] ipc/msg: add msgsnd_timed and msgrcv_timed syscall for system V message queue
From: Arnd Bergmann
Date: Sat Feb 27 2021 - 07:30:28 EST
On Sat, Feb 27, 2021 at 7:52 AM Eric Gao <eric.tech@xxxxxxxxxxx> wrote:
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sometimes, we need the msgsnd or msgrcv syscall can return after a limited
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time, so that the business thread do not be blocked here all the time. In
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this case, I add the msgsnd_timed and msgrcv_timed syscall that with time
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parameter, which has a unit of ms.
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Signed-off-by: Eric Gao <eric.tech@xxxxxxxxxxx>
I have no opinion on whether we want or need this, but I'll have a look
at the implementation, to see if the ABI makes sense.
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index 8fd8c17..42b7db5 100644
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--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
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+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
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@@ -381,3 +381,5 @@
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440 n32 process_madvise sys_process_madvise
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441 n32 epoll_pwait2 compat_sys_epoll_pwait2
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442 n32 mount_setattr sys_mount_setattr
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+443 n32 msgrcv_timed sys_msgrcv_timed
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+444 n32 msgsnd_timed sys_msgsnd_timed
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diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
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index 090d29c..0f1f6ee 100644
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--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
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+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
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@@ -430,3 +430,5 @@
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440 o32 process_madvise sys_process_madvise
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441 o32 epoll_pwait2 sys_epoll_pwait2 compat_sys_epoll_pwait2
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442 o32 mount_setattr sys_mount_setattr
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+443 o32 msgrcv_timed sys_msgrcv_timed
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+444 o32 msgsnd_timed sys_msgsnd_timed
I think mips n32 and o32 both need to use the compat version when running on
a 64-bit kernel, while your patch makes them use the native version.
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@@ -905,7 +906,15 @@ static long do_msgsnd(int msqid, long mtype, void __user *mtext,
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ipc_unlock_object(&msq->q_perm);
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rcu_read_unlock();
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- schedule();
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+
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+ /* sometimes, we need msgsnd syscall return after a given time */
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+ if (timeoutms <= 0) {
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+ schedule();
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+ } else {
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+ timeoutms = schedule_timeout(timeoutms);
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+ if (timeoutms == 0)
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+ timeoutflag = true;
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+ }
I wonder if this should be schedule_timeout_interruptible() or at least
schedule_timeout_killable() instead of schedule_timeout(). If it should,
this should probably be done as a separate change.
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+COMPAT_SYSCALL_DEFINE5(msgsnd_timed, int, msqid, compat_uptr_t, msgp,
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+ compat_ssize_t, msgsz, int, msgflg, compat_long_t, timeoutms)
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+{
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+ struct compat_msgbuf __user *up = compat_ptr(msgp);
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+ compat_long_t mtype;
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+
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+ timeoutms = (timeoutms + 9) / 10;
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+
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+ if (get_user(mtype, &up->mtype))
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+ return -EFAULT;
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+
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+ return do_msgsnd(msqid, mtype, up->mtext, (ssize_t)msgsz, msgflg, (long)timeoutms);
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+}
My preference would be to simplify both the timed and non-timed version by
moving the get_user() into do_msgsnd() and using in_compat_task() to pick
the right type. Same for the receive side of course. If you do this,
watch out for
x32 support, which uses the 64-bit version.
Arnd