Re: [PATCH v17 1/3] proc: add /proc/<pid>/arch_status

On 2019/4/25 5:18, Thomas Gleixner wrote:

On Mon, 22 Apr 2019, Aubrey Li wrote:

quoted

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5ad92419be19..d5a9c5ddd453 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig

@@ -208,6 +208,7 @@ config X86
 	select USER_STACKTRACE_SUPPORT
 	select VIRT_TO_BUS
 	select X86_FEATURE_NAMES		if PROC_FS
+	select PROC_PID_ARCH_STATUS		if PROC_FS

Can you please stop mixing arch and proc code? There is no point in
enabling this on x86 right away.

quoted

+
+config PROC_PID_ARCH_STATUS
+	bool "Enable /proc/<pid>/arch_status file"

Why is this switchable? x86 selects it if PROC_FS is enabled and all other
architectures are absolutely not interested in this.

Above and this, I was trying to avoid an empty arch_file on other architectures.
In previous proposal the entry only exists on the platform with AVX512.

quoted

+	default n
+	help
+	  Provides a way to examine process architecture specific information.
+	  See <file:Documentation/filesystems/proc.txt> for more information.

Which contains zero information about this file when only this patch is
applied. 

quoted

@@ -94,6 +94,7 @@
 #include <linux/sched/debug.h>
 #include <linux/sched/stat.h>
 #include <linux/posix-timers.h>
+#include <linux/processor.h>

That include is required because it does NOT contain anything useful for
this, right?

quoted

+/*
+ * Add support for task architecture specific output in /proc/pid/arch_status.
+ * task_arch_status() must be defined in asm/processor.h
+ */
+#ifdef CONFIG_PROC_PID_ARCH_STATUS
+# ifndef task_arch_status
+# define task_arch_status(m, task)
+# endif

What exactly is the point of this macro mess? If an architecture selects
CONFIG_PROC_PID_ARCH_STATUS then it has to provide proc_task_arch_status()
and the prototype should be in include/linux/proc_fs.h.

I was trying to address Andy's last comments. If we have the prototype in 
include/linux/proc_fs.h, we'll have a weak function definition in fs/proc/array.c,
which bloats other architectures.

In that way proc_task_arch_status() should be defined in asm/processor.h,
but proc_task_arch_status() has four parameters, I don't want unnecessary
"struct pid_namespace *ns" and "struct pid *pid" leaked into arch headers,
so I defined task_arch_status(m, task) to avoid that.

quoted

+static int proc_pid_arch_status(struct seq_file *m, struct pid_namespace *ns,
+				struct pid *pid, struct task_struct *task)
+{
+	task_arch_status(m, task);
+	return 0;
+}
+#endif /* CONFIG_PROC_PID_ARCH_STATUS */

Thanks,

	tglx

Thanks,
-Aubrey