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authorVegard Nossum <vegard.nossum@oracle.com>2015-12-18 21:28:53 +0100
committerRichard Weinberger <richard@nod.at>2016-01-10 21:49:47 +0100
commit0754fb298f2f2719f0393491d010d46cfb25d043 (patch)
tree50e373a0423f25e4707b198b7a5693e169b8cbad
parent9f2dfda2f2f1c6181c3732c16b85c59ab2d195e0 (diff)
uml: flush stdout before forking
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. Cc: stable@vger.kernel.org Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com> Signed-off-by: Richard Weinberger <richard@nod.at>
-rw-r--r--arch/um/os-Linux/start_up.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
index 47f1ff056a54..22a358ef1b0c 100644
--- a/arch/um/os-Linux/start_up.c
+++ b/arch/um/os-Linux/start_up.c
@@ -94,6 +94,8 @@ static int start_ptraced_child(void)
{
int pid, n, status;
+ fflush(stdout);
+
pid = fork();
if (pid == 0)
ptrace_child();