Re: [PATCH] clone.2: Mention that CLONE_PARENT is off-limits for inits
From: Michael Kerrisk (man-pages) <hidden>
Date: 2019-11-21 09:53:59
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Hello Christian, On 11/20/19 11:45 AM, Christian Brauner wrote:
quoted hunk ↗ jump to hunk
From: Christian Brauner <redacted> The CLONE_PARENT flag cannot but used by init processes. Let's mention this in the manpages to prevent suprises. Signed-off-by: Christian Brauner <redacted> --- man2/clone.2 | 7 +++++++ 1 file changed, 7 insertions(+)diff --git a/man2/clone.2 b/man2/clone.2 index f0f29d6f1..aa98ab79b 100644 --- a/man2/clone.2 +++ b/man2/clone.2@@ -646,6 +646,13 @@ if .B CLONE_PARENT is set, then the parent of the calling process, rather than the calling process itself, will be signaled. +.IP +The kernel will not allow global init and init processes in pid +namespaces to use the +.B CLONE_PARENT +flag. This is done to prevent the creation of multi-rooted process +trees. It also avoids unreapable zombies in the initial pid +namespace. .TP .BR CLONE_PARENT_SETTID " (since Linux 2.5.49)" Store the child thread ID at the location pointed to by
Thank. I applied, and then tweaked the text a little, and noted the associated EINVAL error. In the end, the change is as below. Cheers, Michael index 60e746151..382f6b791 100644
--- a/man2/clone.2
+++ b/man2/clone.2@@ -648,6 +648,14 @@ if .B CLONE_PARENT is set, then the parent of the calling process, rather than the calling process itself, will be signaled. +.IP +The +.B CLONE_PARENT +flag can't be used in clone calls by the +global init process (PID 1 in the initial PID namespace) +and init processes in other PID namespaces. +This restriction prevents the creation of multi-rooted process trees +as well as the creation of unreapable zombies in the initial PID namespace. .TP .BR CLONE_PARENT_SETTID " (since Linux 2.5.49)" Store the child thread ID at the location pointed to by
@@ -1273,6 +1281,11 @@ were specified in the .IR flags mask. .TP +.BR EINVAL " (since Linux 2.6.32)" +.\" commit 123be07b0b399670a7cc3d82fef0cb4f93ef885c +.BR CLONE_PARENT +was specified, and the caller is an init process. +.TP .B EINVAL Returned by the glibc .BR clone ()
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Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/