From: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
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: Jiri Slaby <jslaby@xxxxxxx>
---
arch/um/os-Linux/start_up.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
index 337518c5042a..b412c62486f0 100644
--- 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();
--
2.7.2
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