This is a note to let you know that I've just added the patch titled
uml: flush stdout before forking
to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
uml-flush-stdout-before-forking.patch
and it can be found in the queue-3.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 0754fb298f2f2719f0393491d010d46cfb25d043 Mon Sep 17 00:00:00 2001
From: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Date: Fri, 18 Dec 2015 21:28:53 +0100
Subject: uml: flush stdout before forking
From: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
commit 0754fb298f2f2719f0393491d010d46cfb25d043 upstream.
I was seeing some really weird behaviour where piping UML's output
somewhere would cause output to get duplicated:
$ ./vmlinux | head -n 40
Checking that ptrace can change system call numbers...Core dump limits :
soft - 0
hard - NONE
OK
Checking syscall emulation patch for ptrace...Core dump limits :
soft - 0
hard - NONE
OK
Checking advanced syscall emulation patch for ptrace...Core dump limits :
soft - 0
hard - NONE
OK
Core dump limits :
soft - 0
hard - NONE
This is because these tests do a fork() which duplicates the non-empty
stdout buffer, then glibc flushes the duplicated buffer as each child
exits.
A simple workaround is to flush before forking.
Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Signed-off-by: Richard Weinberger <richard@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/um/os-Linux/start_up.c | 2 ++
1 file changed, 2 insertions(+)
--- a/arch/um/os-Linux/start_up.c
+++ b/arch/um/os-Linux/start_up.c
@@ -95,6 +95,8 @@ static int start_ptraced_child(void)
{
int pid, n, status;
+ fflush(stdout);
+
pid = fork();
if (pid == 0)
ptrace_child();
Patches currently in stable-queue which might be from vegard.nossum@xxxxxxxxxx are
queue-3.14/uml-flush-stdout-before-forking.patch
queue-3.14/rds-fix-race-condition-when-sending-a-message-on-unbound-socket.patch
queue-3.14/uml-fix-hostfs-mknod.patch
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