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Date: Tue, 2 Feb 2016 10:14:11 -0800 From: Kamal Mostafa <kamal@...onical.com> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org, kernel-team@...ts.ubuntu.com Cc: Vegard Nossum <vegard.nossum@...cle.com>, Richard Weinberger <richard@....at>, Kamal Mostafa <kamal@...onical.com> Subject: [PATCH 3.13.y-ckt 056/136] uml: flush stdout before forking 3.13.11-ckt34 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ 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: Kamal Mostafa <kamal@...onical.com> --- 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 337518c..b412c62 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(); -- 1.9.1
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