[PATCH v3 1/4] sys_info: add helper for callers that print some sys_info on their own

[Bradley Morgan <include@grrlz.net>]

Some callers print some sys_info on their own before calling sys_info().

Add a helper which would allow to prevent a duplicated output.

It is a bit tricky because kernel_si_mask should be used only
when the call-specific si_mask is empty. But the duplicated
output must be prevented there as well.

Fixes: a9af76a78760 ("watchdog: add sys_info sysctls to dump sys info on system lockup")
Cc: stable@vger.kernel.org
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Bradley Morgan <include@grrlz.net>
---
 include/linux/sys_info.h |  1 +
 lib/sys_info.c           | 20 ++++++++++++++++++--
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/include/linux/sys_info.h b/include/linux/sys_info.h
index a5bc3ea3d44b..f1c2552ca3d1 100644
--- a/include/linux/sys_info.h
+++ b/include/linux/sys_info.h
@@ -18,6 +18,7 @@
 #define SYS_INFO_BLOCKED_TASKS		0x00000080
 
 void sys_info(unsigned long si_mask);
+void sys_info_with_filter(unsigned long si_mask, unsigned long si_ignore_mask);
 unsigned long sys_info_parse_param(char *str);
 
 #ifdef CONFIG_SYSCTL
diff --git a/lib/sys_info.c b/lib/sys_info.c
index f32a06ec9ed4..d411fee10415 100644
--- a/lib/sys_info.c
+++ b/lib/sys_info.c
@@ -136,8 +136,10 @@ static int __init sys_info_sysctl_init(void)
 subsys_initcall(sys_info_sysctl_init);
 #endif
 
-static void __sys_info(unsigned long si_mask)
+static void __sys_info(unsigned long si_mask, unsigned long si_ignore_mask)
 {
+	si_mask &= ~si_ignore_mask;
+
 	if (si_mask & SYS_INFO_TASKS)
 		show_state();
 
@@ -160,7 +162,21 @@ static void __sys_info(unsigned long si_mask)
 		show_state_filter(TASK_UNINTERRUPTIBLE);
 }
 
+void sys_info_with_filter(unsigned long si_mask, unsigned long si_ignore_mask)
+{
+	unsigned long dump_mask = si_mask & ~si_ignore_mask;
+
+	/*
+	 * Do not fall back to kernel_si_mask when the caller context
+	 * required only the ignored information.
+	 */
+	if (si_mask && !dump_mask)
+		return;
+
+	__sys_info(dump_mask ? : kernel_si_mask, si_ignore_mask);
+}
+
 void sys_info(unsigned long si_mask)
 {
-	__sys_info(si_mask ? : kernel_si_mask);
+	sys_info_with_filter(si_mask, 0);
 }
-- 
2.53.0