| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.14 092/130] uml: flush stdout before forking | Date | Tue, 01 Mar 2016 23:53:28 +0000 |
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3.14-stable review patch. If anyone has any objections, please let me know.
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From: Vegard Nossum <vegard.nossum@oracle.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@oracle.com> Signed-off-by: Richard Weinberger <richard@nod.at> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- 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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