This is a note to let you know that I've just added the patch titled uml: flush stdout before forking to the 3.10-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-3.10 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-3.10/uml-flush-stdout-before-forking.patch queue-3.10/rds-fix-race-condition-when-sending-a-message-on-unbound-socket.patch queue-3.10/uml-fix-hostfs-mknod.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html