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Date: Mon, 08 Feb 2016 23:53:51 +0000 From: Ben Hutchings <ben@...adent.org.uk> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org CC: akpm@...ux-foundation.org, "Richard Weinberger" <richard@....at>, "Vegard Nossum" <vegard.nossum@...cle.com> Subject: [PATCH 3.2 38/87] uml: flush stdout before forking 3.2.77-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Vegard Nossum <vegard.nossum@...cle.com> 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@...cle.com> Signed-off-by: Richard Weinberger <richard@....at> Signed-off-by: Ben Hutchings <ben@...adent.org.uk> --- 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();
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