hung_task: Display every hung task warning

When khungtaskd detects hung tasks, it prints out
backtraces from a number of those tasks.

Limiting the number of backtraces being printed
out can result in the user not seeing the information
necessary to debug the issue. The hung_task_warnings
sysctl controls this feature.

This patch makes it possible for hung_task_warnings
to accept a special value to print an unlimited
number of backtraces when khungtaskd detects hung
tasks.

The special value is -1. To use this value it is
necessary to change types from ulong to int.

Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: oleg@redhat.com
Link: http://lkml.kernel.org/r/1390239253-24030-3-git-send-email-atomlin@redhat.com
[ Build warning fix. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 9 insertions, 5 deletions

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 9328b80eaf14..0b9c169d577f 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -37,7 +37,7 @@ int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
  */
 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
 
-unsigned long __read_mostly sysctl_hung_task_warnings = 10;
+int __read_mostly sysctl_hung_task_warnings = 10;
 
 static int __read_mostly did_panic;
 
@@ -98,7 +98,9 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 
         if (!sysctl_hung_task_warnings)
                 return;
-        sysctl_hung_task_warnings--;
+
+        if (sysctl_hung_task_warnings > 0)
+                sysctl_hung_task_warnings--;
 
         /*
          * Ok, the task did not get scheduled for more than 2 minutes,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c398a58673a7..dd5b4496637e 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -122,7 +122,8 @@ extern int blk_iopoll_enabled;
 static int sixty = 60;
 #endif
 
-static int neg_one = -1;
+static int __maybe_unused neg_one = -1;
+
 static int zero;
 static int __maybe_unused one = 1;
 static int __maybe_unused two = 2;
@@ -978,9 +979,10 @@ static struct ctl_table kern_table[] = {
         {
                 .procname       = "hung_task_warnings",
                 .data           = &sysctl_hung_task_warnings,
-                .maxlen         = sizeof(unsigned long),
+                .maxlen         = sizeof(int),
                 .mode           = 0644,
-                .proc_handler   = proc_doulongvec_minmax,
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &neg_one,
         },
 #endif
 #ifdef CONFIG_COMPAT